If you are sure that Excel is running with the workbook open then you don't need create a new instance of Excel:

Sub ScratchMacro()
'A basic Word macro coded by Greg Maxey
 Dim oXLApp As Object
 Dim oWB As Object
  Set oXLApp = GetObject(, "Excel.Application")
  Set oWB = oXLApp.Workbooks("Named Book.xlsx")
  oWB.Activate
lbl_Exit:
  Exit Sub
End Sub