Ran into this bug today while trying to deploy Communicator Web Access 2007 R2 on Windows Server 2008. Apparently the SPN isn’t registered properly during the installation process which causes integrated authentication to fail. After you try to sign in you’ll see this error:
Cannot sign in because your computer clock is not set correctly or your account is invalid.(Error code: 0-1-492)
Jason Shave ran across this same issue a few weeks ago and has a nice explanation on how to add the SPN to your CWAService account.
I had to restart the CWA virtual server before the SPN change took effect, but after that CWA logged in just fine: