An update is available that enables you to join a meeting by using Lync 2010 when proxy authentication is required

This article describes an update that enables Microsoft Lync 2010 users to join a meeting when proxy authentication is required.

• You sign in to Lync 2010 in an organization that has a proxy server deployed.
• The proxy server requires all outgoing Web access requests to be authenticated.
• A Lync 2010 user who is not in a federated organization sends you a meeting invitation. The invitation enables anonymous users to join the meeting.
• You try to join the meeting.

In this scenario, a 407 error is returned form the proxy server. Additionally, you receive the following error message:
 
Note After this update is installed you will be prompted to type in credentials when you try to join a meeting.

To enable users to join meetings when proxy authentication is required, apply the following update:

2791382 Description of the cumulative update package for Lync 2010: March 2013