It looks like you have that as the Entity name for one of your entities in the model? It is a modelling issue in any case.
I've just recently noticed that I get this error upon starting my WO app. Everything seems to be working ok, just wondering if I need to address it:
Oct 27 11:21:44 CRR[49599] ERROR er.extensions.eof.ERXEntityClassDescription - Entity NSMutableDictionary not found in the default model group!