Okay, a couple of random thoguhts. Have you tried repiring/compacting the database? Or, have tried decompiling and recompiling it? I don't know how to decompile from within access, except to call up MSACCESS.EXE from a batch file with a /decompile switch.

C:
CD \PROGRAM FILES\MICROSOFT OFFICE\OFFICE
MSACCESS.EXE /decompile

Recompiling has helped cure any number of wierdnesses, as rogue/junk code can remain hidden from previous compilations.