Borislav
I found the problem and a solution. I had a relation in the data environment of the calling form that linked to the controlSource of the comboBox on the "called form". Deleting the relationship or setting the dataSession property on the "called" form to "private" remedied the problem.

Question for you: Do you generally set the dataSession property to private on your forms? I do on reports, but have not been doing so on reports

thanks, Vince