"Connection is not established" error message in a Lync 2010 client when an attendee is disconnected from an application-sharing session in a large conference

Applies to: Lync 2010

Symptoms


Certain attendees are disconnected from an application-sharing session in a conference if the attendee amount becomes more than 200.Additionally, the disconnected attendees receive the following error message: 

Connection is not established.

Additionally, a retry button is displayed to rejoin the application-sharing session.

Cause


This issue occurs when too many messages are queued in a Remote Desktop Protocol (RDP) API thread. All new connect viewer calls in the Application Sharing Server (ASMCU) are rejected. Therefore, RDP loses certain protocol packets.

Resolution


To resolve this issue, install the following cumulative update:
2496325 Description of the cumulative update package for Lync 2010: April 2011

Status


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.