How to find out Interval from RecurrenceItem in EWS

i created a function which gets all Informations of an appointment item from EWS. I also need the Interval of an RecurrenceItem but it doesnt work. This is what i did:

ExtendedPropertyDefinition PidLidCleanGlobalObjectId = new ExtendedPropertyDefinition(DefaultExtendedPropertySet.Meeting, 0x00000023, MapiPropertyType.Binary);
    ExtendedPropertyDefinition PidLidDayInterval = new ExtendedPropertyDefinition(DefaultExtendedPropertySet.Appointment, 0x00000011, MapiPropertyType.Integer);
    ExtendedPropertyDefinition PidLidWeekInterval = new ExtendedPropertyDefinition(DefaultExtendedPropertySet.Appointment, 0x00000012, MapiPropertyType.Integer);
    ExtendedPropertyDefinition PidLidMonthInterval = new ExtendedPropertyDefinition(DefaultExtendedPropertySet.Appointment, 0x00000013, MapiPropertyType.Integer);
    ExtendedPropertyDefinition PidLidYearInterval = new ExtendedPropertyDefinition(DefaultExtendedPropertySet.Appointment, 0x00000014, MapiPropertyType.Integer);

    PropertySet propset = new PropertySet(PropertySet.FirstClassProperties);
    propset.Add(PidLidCleanGlobalObjectId);
    propset.Add(PidLidDayInterval);
    propset.Add(PidLidWeekInterval);
    propset.Add(PidLidMonthInterval);
    propset.Add(PidLidYearInterval);


FindItemsResults < Item > appointments = esb.FindItems(new FolderId(WellKnownFolderName.Calendar, new Mailbox(room)), searchFilter, view);

            foreach(Appointment appointment in appointments) {

                CalendarObjectClass calobj = new CalendarObjectClass();

                appointment.Load(propset);
                byte[] value = null;
                Int32 interval = 0;

                if (appointment.TryGetProperty(PidLidCleanGlobalObjectId, out value)) {
                    calobj.correlationid = Convert.ToBase64String(value);
                }

                if (calobj.isrecurring) {
                    switch (getRecurrenceType(calobj.recurrence)) {
                        case RecurrenceType.olRecursDaily:
                            {
                                if (appointment.TryGetProperty(PidLidDayInterval, out interval)) {          // this is the right case but it won't set the instance 
                                    calobj.interval = interval;                                             
                                }
                                break;
                                ...
                            }
                            }

i can't get the interval property. What am i doing wrong? is there another way to solve this problem?

PidLidDayInterval was a WebDAV extension property so it won't work in Exchange 2010 or greater. You should just be able to get the interval from the recurrence pattern eg

((Recurrence.DailyPattern)appointment.Recurrence).Interval)

This would only be available on the Master instance object.

Cheers Glen