From Entourage Help:
To help you solve problems you might encounter as you work, Microsoft
Entourage keeps a detailed log of errors that occur, such as problems
connecting to your Internet service provider (ISP), processing mail or
rules, or decoding file attachments. Errors are stored in the Error Log
until you quit Entourage. Each time an error occurs, a description of the
error appears. This description identifies the error and provides a brief
explanation. It can also contain suggestions for fixing the problem. In some
cases, you can also click a button that takes you directly to the source of
the problem so that you can fix it.
€ To view the Error Log, click Error Log on the Window menu. If the Error
Log is unavailable, no errors have occurred since you started Microsoft
Entourage.
€ To open an error description, double-click it.
€ To delete an error description, click it, and then click Delete.
My question: Does your error show up with a description? If so, did you try
the suggested fix?