Note User A and User B are both Microsoft Lync 2010 users. User C is a Microsoft Office Communicator 2007 R2 user.
User A shares an application together with User B and User C.
User A stops to share the application.
User B starts to share an application.
In this scenario, User C is disconnected from the application sharing session during the sharing switch.
This issue occurs because Lync 2010 uses a different events order from Office Communicator 2007 R2. In Office Communicator 2007 R2, when a sharing switch happens, the passive viewer obtains a notification about the new sharing session, and then discovers that the old sharing session has stopped. Therefore, the passive viewer stays in the application sharing session. However, the events come in reverse in Lync 2010. Therefore, when Office Communicator 2007 R2 users interoperates with Lync 2010 users, this issue occurs.
To resolve this problem, install the following update rollup:
2291453 Description of the cumulative update package for Communicator 2007 R2: November 2010
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.