No photo of Luís Manuel Sancho Moniz Pereira

View Scopus Profile

Luís Manuel Sancho Moniz Pereira

Prof

Former affiliation
 https://orcid.org/0000-0001-7880-4322
Calculated based on number of publications stored in Pure and citations from Scopus
1991 …2022

Research activity per year

If you made any changes in Pure these will be visible here soon.
Filter
Conference contribution

Search results

  • 2018

    Intelligent agents via joint tabling of logic program abduction and updating

    Sabili, A. F., Saptawijaya, A. & Pereira, L. M., 4 May 2018, 2017 International Conference on Advanced Computer Science and Information Systems, ICACSIS 2017. Institute of Electrical and Electronics Engineers Inc., p. 465-470 6 p. 8355075. (International Conference on Advanced Computer Science and Information Systems; vol. 2018-January).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Tabling in contextual abduction with answer subsumption

    Perkasa, S. M. A., Saptawijaya, A. & Pereira, L. M., 4 May 2018, 2017 International Conference on Advanced Computer Science and Information Systems, ICACSIS 2017. Institute of Electrical and Electronics Engineers Inc., p. 459-464 6 p. 8355074. (International Conference on Advanced Computer Science and Information Systems; vol. 2018-January).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    4 Citations (Scopus)
  • 2017

    Contextual reasoning: Usually birds can abductively fly

    Saldanha, E. A. D., Hölldobler, S. & Pereira, L. M., 2017, Logic Programming and Nonmonotonic Reasoning - 14th International Conference, LPNMR 2017, Proceedings. Balduccini, M. & Janhunen, T. (eds.). Cham: Springer Verlag, p. 64-77 14 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 10377 LNAI).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    6 Citations (Scopus)

  • Social manifestation of guilt leads to stable cooperation in multi-agent systems

    Pereira, L. M., Lenaerts, T., Martinez-Vaquero, L. A. & Han, T. A., 2017, 16th International Conference on Autonomous Agents and Multiagent Systems, AAMAS 2017. Durfee, E., Winikoff, M., Larson, K. & Das, S. (eds.). International Foundation for Autonomous Agents and Multiagent Systems (IFAAMAS), Vol. 3. p. 1421-1430 10 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    22 Citations (Scopus)
  • 2016

    Conditions for the evolution of apology and forgiveness in populations of autonomous agents

    Lenaerts, T., Martinez-Vaquero, L. A., Han, T. A. & Pereira, L. M., 1 Jan 2016, 2016 AAAI Spring Symposium Series - Collected Papers from the AAAI Spring Symposia. AI Access Foundation, Vol. SS-16-01 - 07. p. 242-248 7 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    1 Citation (Scopus)

  • Emergence of cooperation in group interactions: Avoidance versus restriction

    Han, T. A., Pereira, L. M. & Lenaerts, T., 1 Jan 2016, 2016 AAAI Spring Symposium Series - Collected Papers from the AAAI Spring Symposia. AI Access Foundation, Vol. SS-16-01 - 07. p. 214-216 3 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Guilt for non-humans

    Pereira, L. M., Han, T. A., Martinez-Vaquero, L. & Lenaerts, T., 2016, 2016 AAAI Spring Symposium Series - Collected Papers from the AAAI Spring Symposia. AI Access Foundation, Vol. SS-16-01 - 07. p. 249-252 4 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • 2015

    Logic programming applied to machine ethics

    Saptawijaya, A. & Pereira, L. M., 1 Jan 2015, Progress in Artificial Intelligence - 17th Portuguese Conference on Artificial Intelligence, EPIA 2015, Proceedings. Pereira, F., Machado, P., Costa, E. & Cardoso, A. (eds.). Springer Verlag, p. 414-422 9 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 9273).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    2 Citations (Scopus)
  • 2014

    An abductive reasoning approach to the belief-bias effect

    Pereira, L. M., Dietz, E. A. & Hölldobler, S., 1 Jan 2014, 14th International Conference on the Principles of Knowledge Representation and Reasoning, KR 2014. AAAI Press, p. 653-656 4 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    13 Citations (Scopus)

  • Complex systems of mindful entities: on intention recognition and commitment

    Pereira, L. M., Han, T. A. & Santos, F. C., 1 Jan 2014, Model-Based Reasoning in Science and Technology - Theoretical and Cognitive Issues. Magnani, L. (ed.). Springer International Publishing, p. 499-525 27 p. (Studies in Applied Philosophy, Epistemology and Rational Ethics; vol. 8).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    3 Citations (Scopus)

  • Towards modeling morality computationally with logic programming

    Saptawijaya, A. & Pereira, L. M., 7 Feb 2014, Practical Aspects of Declarative Languages - 16th International Symposium, PADL 2014, Proceedings. p. 104-119 16 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 8324 LNCS).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    13 Citations (Scopus)
  • 2013

    Incremental tabling for query-driven propagation of logic program updates

    Saptawijaya, A. & Pereira, L. M., 2013, Logic for Programming, Artificial Intelligence, and Reasoning - 19th International Conference, LPAR 2013, Proceedings. McMillan, K., Middeldorp, A. & Voronkov, A. (eds.). Springer Verlag, p. 694-709 16 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 8312).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    7 Citations (Scopus)

  • Program Updating by Incremental and Answer Subsumption Tabling

    Saptawijaya, A. & Pereira, L. M., 2013, LOGIC PROGRAMMING AND NONMONOTONIC REASONING (LPNMR 2013). Cabalar, P. & Son, TC. (eds.). SPRINGER-VERLAG BERLIN, p. 479-484 6 p. (Lecture Notes in Computer Science; vol. 8148).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    4 Citations (Scopus)

  • Towards Practical Tabled Abduction in Logic Programs

    Saptawijaya, A. & Pereira, L. M., 2013, PROGRESS IN ARTIFICIAL INTELLIGENCE, EPIA 2013. Correia, L., Reis, LP. & Cascalho, J. (eds.). SPRINGER-VERLAG BERLIN, p. 223-234 12 p. (Lecture Notes in Artificial Intelligence; vol. 8154).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    2 Citations (Scopus)

  • Towards Practical Tabled Abduction Usable in Decision Making

    Saptawijaya, A. & Pereira, L. M., 2013, INTELLIGENT DECISION TECHNOLOGIES. NevesSilva, R., Watada, J., PhillipsWren, G., Jain, LC. & Howlett, RJ. (eds.). IOS Press, p. 429-438 10 p. (Frontiers in Artificial Intelligence and Applications; vol. 255).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    4 Citations (Scopus)

  • Why is it so hard to say sorry? Evolution of apology with commitments in the iterated Prisoner's Dilemma

    Han, T. A., Pereira, L. M., Santos, F. C. & Lenaerts, T., 1 Dec 2013, IJCAI 2013 - Proceedings of the 23rd International Joint Conference on Artificial Intelligence. p. 177-183 7 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    29 Citations (Scopus)
  • 2012

    Abductive Logic Programming with Tabled Abduction

    Pereira, L. M. S. M., 1 Jan 2012, International Conferences on Software Engineering Advances. p. 548-556

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Intention Recognition, Commitment and the Evolution of Cooperation

    Pereira, L. M. S. M., 1 Jan 2012, IEEE World Congress on Computational Intelligence. p. 1-8

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    16 Citations (Scopus)

  • Moral Reasoning Under Uncertainty

    Pereira, L. M. S. M., 1 Jan 2012, The Intl. Conf. on Logic for Programming, Artificial Intelligence and Reasoning (LPAR),. p. 212-227

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    32 Citations (Scopus)

  • The Emergence of Commitments and Cooperation

    Pereira, L. M. S. M., 1 Jan 2012, Intl. Conf. on Autonomous Agents and Multiagent Systems (AAMAS). p. 559-566

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    21 Citations (Scopus)
  • 2011

    Adaptive reasoning for cooperative agents

    Pereira, L. M. & Pinto, A. M., 2011, Applications of Declarative Programming and Knowledge Management - 18th International Conference, INAP 2009, Revised Selected Papers. Abreu, S. & Siepel, D. (eds.). Évora, Portugal, p. 102-116 15 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 6547 LNAI).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    1 Citation (Scopus)

  • Elder Care via Intention Recognition and Evolution Prospection

    DI Group Author & Pereira, L. M., 1 Jan 2011, Lecture Notes in Computer Science. Abreu, S. & Siepel, D. (eds.). Évora, Portugal: Univ. Évora, p. 170-187

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    8 Citations (Scopus)

  • Stabel model implementation of layer supported models by program transformation

    Pereira, L. M. & Pinto, A. M., 2011, Applications of Declarative Programming and Knowledge Management: 18th International Conference, INAP 2009, Revised Selected Papers. Abreu, S. & Seipel, D. (eds.). Berlin: Springer Verlag, p. 70-84 15 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 6547 LNAI).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • The role of intention recognition in the evolution of cooperative behavior

    Han, T. A., Pereira, L. M. & Santos, F. C., 2011, IJCAI 2011 - 22nd International Joint Conference on Artificial Intelligence. p. 1684-1689 6 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    File
    24 Citations (Scopus)
    1 Downloads (Pure)
  • 2010

    Anytime intention recognition via incremental bayesian network reconstruction

    Han, T. A. & Pereira, L. M., 2010, Proactive Assistant Agents: Papers from the AAAI Fall Symposium, Technical Report. Meneguzzi, F. & Oh, J. (eds.). Menlo Park: AI Access Foundation, p. 20-25 6 p. (AAAI Fall Symposium - Technical Report; vol. FS-10-07).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    3 Citations (Scopus)

  • Collective intention recognition and elder care

    Han, T. A. & Pereira, L. M., 2010, Proactive Assistant Agents: Papers from the AAAI Fall Symposium, Technical Report. Meneguzzi, F. & Oh, J. (eds.). Menlo Park: AI Access Foundation, p. 26-31 6 p. (AAAI Fall Symposium - Technical Report; vol. FS-10-07).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    10 Citations (Scopus)

  • Learning and Evolving Agents in User Monitoring and Training

    Costantini, S., Dell'Acqua, P., Pereira, L. M. & Toni, F., 2010, Proceedings Congresso Nazionale, Associazione Italiana per l’Informatica ed il Calcolo Automatico. Inverardi, P. (ed.). Associazione Italiana per l’Informatica ed il Calcolo Automatico - AICA, 10 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Proactive Intention Recognition for Home Ambient Intelligence

    Anh, H. T. & Pereira, L. M., 2010, Workshop Proceedings of the 6th International Conference on Intelligent Environments. López-Cózar, R., Aghajan, H., Augusto, J. C., Cook, D. J., O'Donoghue, J., Callaghan, V., Egerton, S. & Johnson, B. D. (eds.). IOS Press, p. 91-100 10 p. (Ambient intelligence and smart environments; vol. 8).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Prospective storytelling agents

    Lopes, G. & Pereira, L. M., 2010, Practical Aspects of Declarative Languages - 12th International Symposium, PADL 2010, Proceedings. Carro, M. & Peña, R. (eds.). Berlin, Heidelberg: Springer, p. 294-296 3 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 5937 LNCS).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    9 Citations (Scopus)

  • Tight semantics for logic programs

    Pereira, L. M. & Pinto, A. M., 25 Jun 2010, Technical Communications of the 26th International Conference on Logic Programming: ICLP’10, July 16–19, 2010, Edinburgh, UK. Hermenegildo, M. & Schaub, T. (eds.). Leibniz: Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik, Germany, Vol. 7. p. 134-143 10 p. (Leibniz International Proceedings in Informatics, LIPIcs; vol. 7).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    5 Citations (Scopus)
  • 2009

    Evolution prospection

    Pereira, L. M. & Anh, H. T., 2009, New Advances in Intelligent Decision Technologies: Results of the First KES International Symposium IDT 2009. Springer Verlag, p. 51-63 13 p. (Studies in Computational Intelligence; vol. 199).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    67 Citations (Scopus)

  • Evolution Prospection

    Pereira, L. M. & Anh, H. T., 1 Jan 2009, New Advances in Intelligent Decision Technologies: Results of the First KES International Symposium IDT 2009. Nakamatsu, K., Phillips-Wren, G., Jain, L. C. & Howlett, R. J. (eds.). Berlin: Springer, p. 51-63 13 p. (Studies in Computational Intelligence; vol. 199).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Incremental answer completion in the SLG-WAM

    Swift, T., Pinto, A. M. & Moniz Pereira, L., 2009, Logic Programming: 25th International Conference, ICLP 2009, Proceedings. Warren, DS. & Hill, PM. (eds.). Berlin: Springer-Verlag, Vol. 5649. p. 519-524 6 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 5649 LNCS).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    5 Citations (Scopus)

  • Intention recognition via causal bayes networks plus plan generation

    Pereira, L. M. & Anh, H. T., 2009, Progress in Artificial Intelligence: 14th Portuguese Conference on Artificial Intelligence, EPIA 2009, Proceedings. Lopes, LS., Lau, N., Mariano, P. & Rocha, L. (eds.). Springer, Vol. 5816. p. 138-149 12 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 5816 LNAI).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    24 Citations (Scopus)

  • Layered models top-down querying of normal logic programs

    Pereira, L. M. & Pinto, A. M., 2009, Practical Aspects of Declarative Languages: 11th International Symposium, PADL 2009, Savannah, GA, USA, January 19-20, 2009. Proceedings. Gill, A. & Swift, T. (eds.). Berlin: Springer-Verlag, p. 254-268 15 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 5418 LNCS).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    11 Citations (Scopus)

  • Layer supported models of logic programs

    Moniz Pereira, L. & Pinto, A. M., 2009, Logic Programming and Nonmonotonic Reasoning: 10th International Conference, LPNMR 2009, Proceedings. Berlin: Springer-Verlag, p. 450-456 7 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 5753 LNAI).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    7 Citations (Scopus)

  • Modelling probabilistic causation in decision making

    Pereira, L. M. & Ramli, C. K., 2009, New Advances in Intelligent Decision Technologies: Results of the First KES International Symposium IDT 2009. Nakamatsu, K., Phillips-Wren, G., Jain, L. C. & Howlett, R. J. (eds.). Berlin: Springer, p. 85-95 11 p. (Studies in Computational Intelligence; vol. 199).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    1 Citation (Scopus)

  • On preferring and inspecting abductive models

    Pereira, L. M., Dell'Acqua, P. & Lopes, G., 2009, Practical Aspects of Declarative Languages: 11th International Symposium, PADL 2009, Proceedings. Berlin: Springer-Verlag, p. 1-15 15 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 5418 LNCS).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    4 Citations (Scopus)

  • Runtime Verification of Agent Properties

    Costantini, S., Dell'Acqua, P., Pereira, L. M. & Tsintza, P., 1 Jan 2009, Proceedings of INAP 2009: 18th International Conference on Applications of Declarative Programming and Knowledge Management. Abreu, S. & Siepel, D. (eds.). Évora: Universidade de Évora, p. 257-271 15 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Side-effect inspection for decision making

    Pereira, L. M. & Pinto, A. M., 2009, New Advances in Intelligent Decision Technologies: Results of the First KES International Symposium IDT 2009. Nakamatsu, K. (ed.). Berlin: Springer-Verlag, Vol. 199. p. 139-149 11 p. (Studies in Computational Intelligence; vol. 199).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    1 Citation (Scopus)
  • 2008

    Representing a computer science research organization on the ACM computing classification system

    Mirkin, B., Almeida, S. M. D. S. N. M. D. & Pereira, L. M. S. M., 2008, Supplementary Proceedings of the 16th International Conference on Conceptual Structures (ICCS'08). Eklund, P. & Haemmerlé, O. (eds.). CEUR-WS.org, p. 57-65 9 p. (CEUR Workshop Proceedings; vol. 354).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    4 Citations (Scopus)
  • 2007

    Approved models for normal logic programs

    Pereira, L. M. & Pinto, A. M., 1 Jan 2007, Logic for Programming, Artificial Intelligence, and Reasoning - 14th International Conference, LPAR 2007, Proceedings. Springer Verlag, p. 454-468 15 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 4790 LNAI).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    12 Citations (Scopus)
  • 2005

    Revised stable models - A semantics for logic programs

    Pereira, L. M. & Pinto, A. M., 1 Jan 2005, Progress in Artificial Intelligence - 12th Portuguese Conference on Artificial Intelligence, EPIA 2005, Proceedings. Springer Verlag, p. 29-42 14 p. (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); vol. 3808 LNCS).

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    28 Citations (Scopus)
  • 2003

    An evolvable rule-based e-mail agent

    Alferes, J. J. A., Brogi, A., Leite, J. A. C. P. & Pereira, L. M., 1 Jan 2003, Lecture Notes in Computer Science. Vol. 2902. p. 394-408 15 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    5 Citations (Scopus)

  • An Evolving Agent with EVOLP

    Alferes, J. J. A., Brogi, A., Leite, J. A. C. P. & Pereira, L. M., 1 Jan 2003, Declarative Programming. p. 205-216

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

  • Logic programming for evolving agents

    Alferes, J. J. A., Brogi, A., Leite, J. A. C. P. & Pereira, L. M., 1 Jan 2003, Lecture Notes in Computer Science. Vol. 2782. p. 281-297 17 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    8 Citations (Scopus)

  • Semantic Web Logic Programming tools

    Alferes, J. J. A., Damásio, C. A. I. P. V. & Pereira, L. M., 1 Jan 2003, Lecture Notes in Computer Science. Vol. 2901. p. 16-32 17 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    15 Citations (Scopus)
  • 2002

    A compilation of updates plus preferences

    Alferes, J. J. A., Dell’ Acqua, P. & Pereira, L. M., 1 Jan 2002, Lecture Notes in Artificial Intelligence. Vol. 2424 LNAI. p. 62-74 13 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    12 Citations (Scopus)

  • Computing environment-aware agent behaviours with logic program updates

    Alferes, J. J. A., Brogi, A., Leite, J. A. C. P. & Pereira, L. M., 1 Jan 2002, Lecture Notes in Computer Science. Vol. 2372. p. 216-232 17 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    4 Citations (Scopus)

  • Evolving logic programs

    Alferes, J. J. A., Brogi, A., Leite, J. A. C. P. & Pereira, L. M., 1 Jan 2002, Lecture Notes in Computer Science. Vol. 2424 LNAI. p. 50-62 13 p.

    Research output: Chapter in Book/Report/Conference proceeding › Conference contribution › peer-review

    Open Access
    83 Citations (Scopus)
Your message has successfully been sent.
Your message was not sent due to an error.