public Event UpdateRecurrentEvents(Event calendarEvent)
        {
        Appointment recurringMaster = null;

        // Get the Appoinment by Id
        Appointment appointment = FindItem(calendarEvent.EventId.UniqueId);
        var properties = GetLoadProperties(CalendarEventLightweightType.None);
        appointment.Load(properties);
        if (appointment == null)
        {
            throw new ResourceNotFoundException("Exchange: Appointment was not found in the organizer's calendar.");
        }

        // the code is the same like in the link

        // Update the series.
        try
        {
            // This method results in a call to EWS.
            recurringMaster.Update(ConflictResolutionMode.AutoResolve,
                meeting == null
                    ? SendInvitationsOrCancellationsMode.SendToNone
                    : SendInvitationsOrCancellationsMode.SendToAllAndSaveCopy);

            properties = GetLoadProperties(CalendarEventLightweightType.None);
            recurringMaster.Load(properties);

            recurringMaster.TryGetProperty(extendedPlainTextBody, out plainTextBody);
        }
        catch (Exception ex)
        {
            Log.ErrorFormat("Exchange service error: {0}.", ex.Message);
            throw new GatewayServiceException("Exchange service error", ex);
        }

        return //custom mapper
    }

at Microsoft.Exchange.WebServices.Data.ServiceResponse.InternalThrowIfNecessary()
   at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
   at Microsoft.Exchange.WebServices.Data.ExchangeService.InternalUpdateItems(IEnumerable`1 items, FolderId savedItemsDestinationFolderId, ConflictResolutionMode conflictResolution, Nullable`1 messageDisposition, Nullable`1 sendInvitationsOrCancellationsMode, ServiceErrorHandling errorHandling, Boolean suppressReadReceipt)
   at Microsoft.Exchange.WebServices.Data.ExchangeService.UpdateItem(Item item, FolderId savedItemsDestinationFolderId, ConflictResolutionMode conflictResolution, Nullable`1 messageDisposition, Nullable`1 sendInvitationsOrCancellationsMode, Boolean suppressReadReceipts)
   at Microsoft.Exchange.WebServices.Data.Item.InternalUpdate(FolderId parentFolderId, ConflictResolutionMode conflictResolutionMode, Nullable`1 messageDisposition, Nullable`1 sendInvitationsOrCancellationsMode, Boolean suppressReadReceipts)
   at Microsoft.Exchange.WebServices.Data.Item.Update(ConflictResolutionMode conflictResolutionMode, Boolean suppressReadReceipts)
   at Microsoft.Exchange.WebServices.Data.Item.Update(ConflictResolutionMode conflictResolutionMode)