After Update error

[SAC]

Access 2000 - updated

I'm getting the following error on a form:

The expression After Update you entered as the event property setting
produced the following error: Procedure declaration does not match
description of event or procedure having the same name.

I've erased everything and put a very simple msgbox into the after update
event and I still get this error.

Any ideas on how to fix it?

Thanks.