Private Sub Worksheet_Change(ByVal T As Range)
Dim rng
Set rng = Range(Cells(14, "E"), Cells(Rows.Count, "E").End(3))
If T.Address = "$E$7" And Len(T) Then
If Not IsError(Application.Match(T, rng, 0)) Then
MsgBox "Veuillez saisir un autre numéro, svp", vbCritical, "Numéro de facture déjà existant!"
T = ""
End If
End If
End Sub