Gary,

Have you tried copying the form to a new name, and then eliminate controls one at a time, or start a new form and copy controls onto it one at a time and see when it begins working (or breaks) to see if it's one control causing the issue?

>Thanks for thinking about this and for your suggestions. This is a real puzzler. I suspect I'll dink around with it for quite a while and figure out some sort of kludge that makes it more reliable and never really know the real cause.