title: EWS API 2013 Calendar: The specified folder could not be found in the store
body: <p>With Exchange 2013 EWS API in C#, trying to create an appointment in the calendar of another user, as follows:</p>
  
  <pre><code>var mailbox = new Mailbox("xyz@xyz.com");
  var folderId = new FolderId(WellKnownFolderName.Calendar, mailbox);
  var appointment = new Appointment(service);
  appointment....//etc
  appointment.Save(folderId, SendInvitationsMode.SendToAllAndSaveCopy);
  </code></pre>
  
  <p>This works if we create the appointment via the administrators calendar, but not when we specify the account of another user that was created through the Exchange Admin Center (ECP).  We get the error:</p>
  
  <pre><code>The specified folder could not be found in the store.
  </code></pre>
  
  <p>Apparently this is a permissions issue, but where is this permission set?</p>