>If the name of your object is MyObject, than:
>
>if type("ThisForm.MyObject") = "O" and (ThisForm.MyObject <> NULL)
> *-- The object already exists
>else
> *-- The object doesn't exists
>endif

Syntax check:

Can you say "x = .NULL."? My equivalent, which I know works is:

IF TYPE("ThisForm.MyObject") = "O" .AND. IsNull(ThisForm.MyObject)
*-- The object already exists
ELSE
*-- The object doesn't exists
ENDIF