Try clearing the Form Cache.  You neglected to include yout Outlook version,
something you should ALWAYS include when you post a question.  For Outlook
2003, click this: Tools>Options>Other>Advanced Options>Custom Forms>Manage
Forms>Clear Cache.  Alrernatively, with Outlook closed, you should also be
able to delete the file
%UserProfile%\Local Settings\Application Data\Microsoft\Forms\FRMCACHE.DAT