Mylenium’s After Effects Error Code Database has been updated with more obscure goodness. Some of the entries reflect tech notes at Adobe, but it's nice to have the errors listed in one place.
Also very handy is Troubleshooting After Effects (all versions) at General Specialist. See also the previous entry What do to when AE crashes, which was really relaying a request for using the Crash Reporter, which you wouldn't see with error dialogs but only if AE crashes. That said, AE is a remarkably stable and accurate application.
Update: Todd Kopriva added advice to Mylenium's plea for common sense on forums.