Article ID: 2448003
Consider the following scenario:
This issue occurs because the Multipoint Conferencing Unit does not add the conference URI in the contact header. This behavior causes the session to expire. Therefore, the Multipoint Conferencing Unit disconnects the application sharing session with the external user.
To resolve this problem, install the following cumulative update:
(http://support.microsoft.com/kb/2291724/ )Description of the cumulative update for Office Communications Server 2007 R2, Unified Communications Managed API 2.0 Core Redist 64-bit: November 2010
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.