Private Sub Workbook_Open()
On Error GoTo Fehler
Dim Datum1 As Date
Dim Datum2 As Date
Range("A2").Select
Datum1 = CDate(ActiveCell.Text)
Range("F1").Select
Datum2 = CDate(ActiveCell.Text)
If Datum1 < Datum2 Then
    Range("A2").Select
    ActiveCell.Clear
End If
Fehler:
Range("A1").Select
End Sub