Private Sub ctbAEDVon_Validate(Cancel As Boolean)
  Cancel = Not M_Form.sevEingabeDatumOK(Me.ctbAEDVon, True)
End Sub

Public Function sevEingabeDatumOK(ByRef aTxtBox As sevText, _
                                  Optional ByVal NullWertErlaubt As Boolean = _
                                  False) As Boolean
  sevEingabeDatumOK = True
 
  If aTxtBox.Text = "  .  .    " Then aTxtBox.Text = ""
  If NullWertErlaubt And Len(aTxtBox.Text) = 0 Then Exit Function
 
  Call aTxtBox.SetValue(aTxtBox.Text)
  sevEingabeDatumOK = aTxtBox.IsValidDate()
End Function