Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
If Target.Address = "$C$3" And Sh.[c3] <> "" Then
For Each Sh In ThisWorkbook.Worksheets
If Sh.Name = Target.Value And Sh.Name <> ActiveSheet.Name Then
MsgBox "Unefeuille de ce nom est déjà existante", 64, "Information"
Exit Sub
End If
Next
ActiveSheet.Name = Target.Value
End If
End Sub