title: Exchange Webservices (EWS) UpdateItems error 503
body: <p>if i try to update more than one appointment with the Service.UpdateItems methode the server returns an 503 error.
  My Code:</p>
  
  <pre><code>service.UpdateItems(appointments,folderID,ConflictResolutionMode.AutoResolve, null, SendInvitationsOrCancellationsMode.SendToNone);
  </code></pre>
  
  <p>Updating a single appointment with the Appointment.Update methode works.</p>
  
  <p>Has anyone an idea why Service.UpdateItems does not work ? </p>