如下，判断指定的excel文件是否打开，如果打开，则关闭。但关闭时出错”下标越界

如下，判断指定的excel文件是否打开，如果打开，则关闭。但关闭时出错”下标越界“，请大侠帮忙解决一下，谢谢。

Sub test()
  Dim f As String
  f = "C:\Users\Administrator\Desktop\test.xlsx"
  bl = IsFileOpen(f)
  If bl Then
    MsgBox "打开"
    Excel.Workbooks("test.xlsx").Close False
  Else
    MsgBox "没有打开"
  End If
end sub

Function IsFileOpen(filename As String) As Boolean
      Dim filenum As Integer, errnum As Integer
      On Error Resume Next
      filenum = FreeFile()
      Open filename For Input Lock Read As #filenum
      Close filenum
      errnum = Err
      On Error GoTo 0
      Select Case errnum
          Case 0: IsFileOpen = False
          Case 70: IsFileOpen = True
          Case Else: Error errnum
      End Select
  End Function