Consider the following scenario:
- A proxy server that requires all outgoing web access requests to be authenticated is deployed in an organization.
- You sign in to Microsoft Lync 2010.
- A Lync 2010 user in a non-federated organization sends you a meeting invitation. The invitation enables anonymous users to join the meeting.
- You try to join the meeting.
Cannot sign in because the server is temporarily unavailable.
error ID 28 (source ID 238).
error ID 28 (source ID 238).