Public Beenden As Boolean = False

Private Sub cmdBeenden_Click (ByVal sender AS System.Object ByVal e As _
  System.EventArgs) handles cmdBeenden.Click
Beenden = True
Me.Close
End Sub

Private Sub Form1_Closing (ByVal sender As object, ByVal e As _
  System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
If Beenden = False Then 
   e.cancel = true
End If
End Sub