Code:
...
Dim fs As Object
Dim fo As Object
Dim strTargetSheet As String
...
Set fs = CreateObject("Excel.Application")
Set fo = fs.Workbooks.Add
fo.Sheets("Sheet1").Name = strTargetSheet
...
fo.Sheets(strTargetSheet).Columns("F").NumberFormat = "dd.mm.yyyy"
...
The format of column F is "dd\.mm\.yyyy" instead of "dd.mm.yyyy"!