With Selection.Validation
.Add Type:=xlValidateCustom, AlertStyle:=xlValidAlertStop, Operator:= _
xlBetween, Formula1:="=false"
.IgnoreBlank = True
.InCellDropdown = True
.InputTitle = "Ne pas modifier"
.ErrorTitle = "Ne pas modifier"
.ErrorMessage = "Vous ne pouvez pas modifier cette case"
End With