Min und Max Wert finden funktioniert nic

Sub test()
Dim wksArchiv As Worksheet
Dim ArchivMax As String, ArchivMin As String, AufNr As String
Set wksArchiv = Workbooks("Archiv_Datei.xlsm").Sheets("Daten")
With wksArchiv
ArchivMax = Application.WorksheetFunction.Max(Range("A:A"))
ArchivMin = Application.WorksheetFunction.Min(Range("A:A"))
End With
Range("B7") = ArchivMin
Range("B8") = ArchivMax
End Sub