Laufzeitfehler 13 - Typen unverträglich / Uhrzeit

Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
Dim s%, m%
If Target.Column = 20 Then Exit Sub
With Cells(Target.Row, Target.Column)
If .Value = "" Then Exit Sub
ActiveSheet.Unprotect ("xxx")
If IsNumeric(.Value) And InStr(.Value, ":") = 0 And _
InStr(.Value, ",") = 0 Then
.NumberFormat = "[hh]:mm"
If Len(.Value) > 2 Then
s = Left(.Value, Len(.Value) - 2)
m = Right(.Value, 2)
Else
s = .Value
m = 0
End If
.Value = s & ":" & m
End If
ActiveSheet.Protect ("xxx")
End With
End Sub