Andrea
Option Explicit
Dim WBAktuell As Workbook
Dim WB As Workbook
Sub test()
Set WBAktuell = Thisworkbook
WBAktuell.Activate
On Error Resume Next
Set WB = "Alte.xls"
On Error GoTo 0
If WB Is Nothing Then Set WB = Workbooks.Open("C:\....\Alte.xls")
WB.Activate
'wbAktuell.Activate
'Windows.CompareSideBySideWith WB
End Sub