Marcia,

Actually you were quite helpful. The suggestion to gradually remove stuff from the form until the problem went away was good. I elected to go the other route, i.e. create a new form and gradually add stuff until the problem reappears.

I've had a good start: A new blank form with my subclass of the TreeView control plus a copy of the Init code that populates the TreeView from the problem form. Set WindowType to Modal for this form, and for the caller.

And, this works OK.

Now to add more stuff.

Thanks again for taking the time to help.

Jim