EWS 2010_SP2 and AllDayEvent

Hi,

I created a Event Handler in C#, and it's works good in Exchange2007_SP1,

but my client use Exchange2010_SP2 and not working the AllDayEvent = true.

I don't no who is the problem in this version.

My code:

ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2010_SP2, TimeZoneInfo.Local);

appointmentItem.Subject = nev;
appointmentItem.Start = Convert.ToDateTime(item["Start"]);
appointmentItem.End = Convert.ToDateTime(item["End"]);
appointmentItem.IsAllDayEvent = true;

appointmentItem.Save(SendInvitationsMode.SendOnlyToAll);

Please help!

Thanks,

Niki