>>OK, but it does not tell me what field they are talking about. The form opens and looks OK.

Either you can look around and see if you can find it...

or...

Open the form an Save it under a new name. Start removing controls and seeing if you get the message. You should be able to narrow it down to just the control that's causing the problem. If you remove all the controls and still get the error it's a property of the form.