Submit button fires twice with Forms Authentication

I've got a Forms Authentication login form.  Works nearly perfectly, except that the Button_Submit () event is firing twice.  i checked the Source to make sure I didn't have a handler there for the OnClick() event.  I've got a Handles statement in the method definition (see below).  Is that not needed for Forms Authentication?? 

Private Sub btnSubmit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
 
End Sub
Any ideas anyone?  Thanks, Alex

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