message d'erreur sur ouverture fichier via listbox ?

Private Sub Bouton2_Click()
TextBox4.Value = Workbooks("test.xls").Sheets("Instructions").Range("A5").Value
TextBox4.BackColor = &HFFFF&
With Me.Listbox1
    For i = 0 To Me.Listbox1.ListCount - 1
        If .Selected(i) Then
        On Error Resume Next
            Workbooks.Open (path & .List(i))
            If Err <> 0 Then
                MsgBox "ça ne sert a rien d'ouvrir deux fois le même fichier !"
                On Error GoTo 0
            End If
        End If
    Next i
End With
End Sub

Function Test_Fichier(Fich As String) As Boolean
Dim Wb As Workbook
On Error Resume Next
Set Wb = Workbooks(Fich)
 If Err = 0 Then
   Test_Fichier = True
 Else
   Test_Fichier = False
 End If
End Function

Private Sub CommandButton1_Click()
Dim i As Integer

TextBox4.Value = Workbooks("test.xls").Sheets("Instructions").Range("A5").Value
TextBox4.BackColor = &HFFFF&
With Me.ListBox1
    For i = 0 To Me.ListBox1.ListCount - 1
        If .Selected(i) Then
            If Test_Fichier(Dir(.List(i))) = False Then
              Workbooks.Open (.List(i))
            Else
              MsgBox "Fichier déjà ouvert"
            End If
        End If
    Next i
End With

End Sub