>>>Ali, Don't forget to to set this property to NULL before you close the form. If you forget (like me in this code) the form wouldn't close.
>>>Thanks Nadya.
>>
>>Reset to NULL is not necessary.
>
>Just in case and as I said toNadya it prevents some wrong results if you forget to set it to form.ActiveControl in When event of the control

I say that it is not necessary set it to NULL in order to close the form.