I also write ActiveX controls for the VFP. In VFP manu controls do not work properly and you must write special code to accomplish successful work.

First, make sure error is not caused by bug in the VFP code, from which control is used. Look at error message - if caption contains "Visual Basic" or some like this, error is in the control, otherwise - in VFP code.

If error is in the control, put MsgBox-es at the begin and the end of every procedure. This will help to find place of your error. Best way is writting in LOG-file instead of disolaying MsgBox, but this requires little more code.