Activity models are maintained on a plurality of computers on a network. When a user or a particular activity model at a computer discovers an error, it may query its own activity model to determine a possible source of the error. If it is determined to not be the likely source of the error, the activity model queries the activity models of those computers on the network that it depends on. These activity models may then query the activity models of the computers that their particular host computer depends on and so forth. Ultimately the results of these activity model queries may be used to diagnose the likely source of the error and may be presented to the requesting user as a report.