Try this:

   Dim xlApp As Object
   Dim MySheet As Object
   Dim MyFile As Object
   Dim lngSheet As Long

   Set xlApp = CreateObject("Excel.Application")
   Set MyFile = xlApp.WorkBooks.Open(FileName)

   For lngSheet = 0 To MyFile.Worksheets.Count - 1
       If MyFile.Worksheets(lngSheet).Name = SheetName.Value Then
           Set MySheet = MyFile.Worksheets(lngSheet)
           Exit For
       End If
   Next lngSheet

   If MySheet Is Nothing Then
       ' there is no such sheet in the file
       ' do what you need to do....
   Else
       ' there is such a sheet in the file
       (...)
   End If

   Set MySheet = Nothing
   MyFile.Application.ActiveWorkBook.Close False
   Set MyFile = Nothing
   xlApp.Quit
   Set xlApp = Nothing

   Set rstDebit = Nothing