Question : Communicator 2007 R2 - randomly won't logon

I have office communications server 2007 R2 standard on my network.  I have Communicator 2007 R2 deployed to my office of about 25 users.

For the past month or two, there is an issue that appears to randomly happen.  A user will boot up their computer, then when communicator starts, it asks them for credentials to connect.   Even if they put their correct password, it says the password is incorrect. Usually communicator auto-logs in.
The only way to fix the problem is to reboot.  Sometimes 1 reboot won't fix it, and almost always rebooting again fixes it.
I have done numerous Google searches and not found any good troubleshooting information.

This problem has randomly happened to 10+ users.  It is never consistent.  One week it will work fine, the next, it may happen on 2 separate days.

Answer : Communicator 2007 R2 - randomly won't logon

Well, I finally solved my own problem.  I was checking the tracing log and I noticed the below entry:

ms-diagnostics: 1013;reason="Significant time skew detected during authentication";source="(OCS Server)"

I then went to one of my domain controllers and checked the time.  It was 8 minutes fast.  Once I corrected the time, communicator logged right in without a problem.
Not all domain controllers had the wrong time, so that explains why rebooting sometimes fixed it.