I run Office Communicator 2007 R2. It has been a bit finicky for me as a Microsoft security patch can break it (go figure).
If you install MS09-056 (aka KB974571), you will get an error that the Front-End service will not start with error code 1008124893. That's easy enough to fix, uninstall the hotfix and restart, and the problem is gone. I inadvertently applied that patch more than once, but a second mistake got me in the habit of avoiding that patch and keeping the server running.
When it came to apply Windows Server 2008 R2 Service Pack 1, however, the issue again returned. How could I remove the hotfix when it was a part of a service pack?
Googling the matter again, I came upon an alternative solution that worked for me.
http://support.microsoft.com/kb/982021
Item 5a includes file OCSASNFix.exe. This makes a quick registry fix. I have to confess that I originally manually applied the registry fix, and didn't get the desired result. Running this file, however, restored me to good working service.
