Private Sub TextBox1_Validating(ByVal sender As System.Object, ByVal e As _
      System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating, _
      TextBox2.Validating
        Dim txt As TextBox = CType(sender, TextBox)
        If Not IsNumeric(txt.Text) Then
            MessageBox.Show("Keine gültige Zahl")
        End If
        'e.Cancel = Not IsNumeric(txt.Text)
    End Sub