Karl,
I ran into the same problem (or one that sounds similar) a while back and here's the problem. Your database sounds like it's corrupted.
1. Close your database
2. Open a new blank database.
3. Choose "Get External Data" from the File Menu
4. Import your old database into the new one.
5. Choose select all on all tabs of the import dialog.
Your new database is now an exact copy of the old one and the corruption should get cleaned out during the import.
Good Luck,
Grant.