Consider the following scenario:
A Microsoft Office Communicator 2007 R2 user invites a Microsoft Lync 2010 user to an Audio/Video conference by using the telephone number of the Lync 2010 user.
The Lync 2010 user joins the conference successfully, and then they both end the Audio/Video session without ending the instant message session.
The Office Communicator 2007 R2 user tries to invite the same Lync 2010 user to an Audio/Video conference also by using the telephone number of the Lync 2010 user.
In this scenario, the Lync 2010 user cannot be added to the new Audio/Video conference.
Note This issue may also occur between only Office Communications Server 2007 R2 users.
This issue occurs because the Audio Video Multipoint Conferencing Unit (AVMCU) only removes the asserted identity and leaves the TEL URI in the participant list when users who are invited by using telephone numbers are removed from the conference. Therefore, other requests of adding the same TEL URI fails.
To fix this problem, install the following cumulative update:
2403679 Description of the cumulative update package for Office Communications Server 2007 R2, Audio/Video Conferencing Server: November 2010
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.