Vérifier qu'un fichier n'est pas ouvert

Public Etat As Boolean
Sub OuvrirFichier()
    Dim FileToOpen As String
    FileToOpen = "C:\Excel\Caller.xls"
    Etat = IsFileOpen(FileToOpen)
    If Etat = False Then
    Workbooks.Open FileToOpen
    Else
    MsgBox "Le classeur est déjà ouvert."
    End If
End Sub

Function IsFileOpen(Filename As String)
    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
    End Select
End Function

Sub Test()
Dim Classeur As Workbook
For Each Classeur In Application.Workbooks
If Classeur.Name = "Mon Classeur.xls" Then
MsgBox "Mon Classeur.xls est ouvert"
Exit Sub
End If
Next Classeur
MsgBox "Mon Classeur.xls est fermé"
End Sub

 Etat = IsFileOpen(FileToOpen)

Sub TestErreur()
    MsgBox Err = 0
    MsgBox Err = 70
End Sub

Function IsFileOpen(Filename As String)
'Excel:Check If a File Is Already Open
'Ease of Use :Easy
'Version tested with 2000
'Submitted by: xld
'Description:
'Simple function that checks whether a file is already open within the host application,
'returning True or 'False accordingly.
'Discussion:
'Good programming practice suggests that it is wise to check before taking certain actions.
'One such 'check is before opening a file,
'check whether it is already open or not.
'The code below provides a 'simple function that does this, returning True or False.
'There is also a very simple test program to 'demonstrate the function in use.
'It is possible to run the function from a worksheet formula
'(=IsFileOpen("C:\MyTest\volker2.xls")) although I struggle to see any valid use of this.
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
End Select
End Function

Function IsFileOpen(Filename As String)
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
IsFileOpen = Errnum = 70
End Function