Accessing this property either using app.Properties[AppointmentProperty.MeetingOrganizerName] or app.MeetingOrganizerName throws an exception of type 'System.Runtime.InteropServices.COMException'  RESULT of 0x80070006.  I think this is the COM Error code for invalid handle.  Other Appointment functions Update, Send, etc.. are working.  I'm testing on a WM 5.0 SmartPhone. 

I've found that this issue only seems to occur with appointments that have been retrieved by calling GetOccurrance() on a reoccuring appointment.  

Although it is not documented I think this property (and some of the other extended properties) are only present on the parent appointment not the recurring instances of a series.

Peter