Private Sub Text1_KeyUp(KeyCode As Integer, Shift As Integer)
    If Len(Text1) = 13 And IsNumeric(Text1) Then
        Command1.Enabled = True
    Else
        Command1.Enabled = False
    End If
End Sub

Gru? Michi aus Hannover

1 + 1 = 3 f?r hinreichend gro?e 1