Intermittently, you may be unable to join a multiparty Instant Messaging (IM) conference in Microsoft Office Communications Server 2007 R2. Additionally, those who are on the conference are disconnected from the IM conference.
This problem may occur when Session Initiation Protocol (SIP) transactions time out. If you work in a protected network environment in which you have no connection to the Internet (caged environment) and you have certificates that contain a Certificate Revocation List (CRL) Distribution Point (CDP) that points to a public site, SChannel may take more than 32 seconds to try to download the CRL or to detect that the CDP cannot be accessed. Therefore, SIP transactions time out. When you work in a protected network environment, the CRL check is not required.
To resolve this problem, apply update 974007, and then add the DisableCrlChecks key to the applications configuration file.
For more information about update 974007, click the following article number to view the article in the Microsoft Knowledge Base:
974007 Description of the Cumulative Update for Office Communications Server 2007 R2, Unified Communications Managed API 2.0 Core Redist 64-bit: October 2009
To add the DisableCrlChecks key, add the following code to the "<appSettings>" section of the applications configuration file:
<add key="DisableCrlChecks" value="1" />
For example, the applications configuration file should resemble the following: