Das COM-Objekt des Typs "System.__ComObject" kann nicht in den _
  Schnittstellentyp "Microsoft.Office.Interop.Excel.Application" umgewandelt _
  werden......

Private Sub btnWerteSchreiben_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btnWerteSchreiben.Click
        Dim Exc1 As Microsoft.Office.Interop.Excel.Application
        Dim Exc2 As Microsoft.Office.Interop.Excel.Application
        Dim i As Integer
        Exc1 = GetObject(CurDir() & "\Mappe1.xls")
        Exc2 = GetObject(CurDir() & "\Mappe2.xls")
        For i = 0 To 7
            Exc2.worksheets(1).cells(1, i + 1).Value = _
            Exc1.Worksheets(1).Cells(1, i + 1).Value
        Next
End Sub