If you use Kaspersky with Microsoft Lync (or OCS 2007), you may be interested to know that Kaspersky can kill Lync's connectivity. Specifically, Kapersky Internet Security's network traffic monitor, called Web Protection in some versions blocks the network traffic. It can kill remote desktop sharing sessions (Microsoft Live Meeting sessions) within OCS/Lync, as well as audio/VoIP, and video. Curse you anti-virus! The solution is to disable Kaspersky from scanning communicator.exe (%Program Files%\Microsoft Lync\communicator.exe), essentially making it a trusted application.

OCS Guy also encountered this issue with Microsoft Office Live Meeting, and he too explains the problem and resolution, which was to disable scanning of Microsoft Office Live Meeting's traffic: The firewall wasn’t on, but anti-virus was (as it should be), in this case it was Kaspersky Internet Security 2010.   Alan disabled Kaspersky and re-joined the meeting and we were both able to connect to the audio/video feed.  Alan spent a few minutes digging through Kaspersky and found the setting that was causing the issue, a quick modification to the Kaspersky settings (as shown below) and everything was working as expected.