Form Freezes After Modification

Utilizing Access 2000 I have a form which has a subform. When I make changes to the mainform I can save the change and switch back to form view. Although I can move the cursor from field to field some of the functions do not work at all. For instance I have a field on the main form that is visible depending on the value in another field and likewise the subform is visible depending on the value of that optional field. I can change the value of these fields but the "Event" action does not work. The form is essentially frozen and will not even allow me to use the "X" box to close. I have to use "File; Exit" to close and I have to do that in order to close Access. I can then reopen the database and the changes I made are good and the other fields work OK. This occurs only afte making design changes. The only problem is that it gets very aggravating trying to make design changes.

Any ideas?