We have enabled approx 440 users but this is the first with the problem, he receives below error, we have verified that we can see him in OC server and also there is a SIP address on this user as all others
"Cannot sign into Communicator because this sign-in address was not found"
http://social.microsoft.com/Forums/is/communicationsserveruser/thread/bd823d77-1da8-4dff-829c-4ed3a343ff72