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?

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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