Can't retrieve Appointment.StartTimeZone through EWS Managed API on Exchange 2007 SP1

I can retrieve the Appointment.TimeZone for items with:

PropertySet propertiesAll = new PropertySet(BasePropertySet.IdOnly, ..., AppointmentSchema.TimeZone, AppointmentSchema.StartTimeZone, ...);
ServiceResponseCollection<ServiceResponse> response = Exchange.LoadPropertiesForItems(items, propertiesAll);

But not Appointment.StartTimeZone which returns null.

Appointment.TimeZone is string and seems to be comparable to DisplayName of TimeZoneInfo objects, but unfortunately this seems to b开发者_运维问答e in the language of the end users (in our environment I encountered different languages returned by Exchange for different appointments). So it seems to be complicated/impossible to make proper use of TimeZone string for an appointment.

The main question is, what could result StartTimeZone of an appointment to be null?

Unfortunately, Exchange 2007 SP1 does not support the StartTimeZone property of EWS. If you want to use that property, you must use Exchange 2010.

Sorry I couldn't be of any more help