Private Sub Worksheet_Change(ByVal Target As Range)
If Not Application.Intersect(Target, Range("C2:C26")) Is Nothing Then
If IsEmpty(Target.Value) = True Then Exit Sub
If IsDate(Format(Target.Value, "dd/mm/yyyy")) = False Then
MsgBox ("please enter a valid date format, e.g. 10 sep 2007")
Target.Value = "" 'j`efface la saisie
End If
End If
End Sub