>When I use the following “_Screen.ActiveForm.ActiveControl” I get an error message which states that the "Active.Control" is not an object. So How do I find out what the active control is (during run time)?

Andy, there may be no ActiveControl in the form, or may be no form active at the moment.

.ActiveControl points you to the control which has the focus. As an example:
.ActiveControl just doesn't work in When event. The control doesn't become ActiveControl until When returns .T. and it's GotFocus fired. So, there are moments when you cannot get the .ActiveControl object reference.

It is better to always wrap any .ActiveControl... references into IF like this:

IF TYPE("_screen.ActiveForm.ActiveControl") = "O" AND !ISNULL("_screen.ActiveForm.ActiveControl")
* your code here.
ENDIF

Also, in VFP 6 you should use TYPE() function rather than VARTYPE() because VARTYPE() can choke if the object is unknown.