The problem is happening so far on three Windows 7 computers that used to be able to open Lync, but not anymore. Click the program icon to launch the program and the sign in box appears but Lync stalls at contacting server and signing in. A Lync message appears, "Cannot sign in because the server is temporarily unavailable. If the problem continues, please contact your support team."
Steps taken to resolve
1) Verified the certificate hadn’t expired
2) Deleted communicator folders in both folder locations, c:\users\username\app data\local\microsoft and c:\users\username\app data\roaming\microsoft
3) Deleted the SSID folders
4) Tried the manual configuration to connect to Lync by entering the sip domain name for the internal and external server names
5) Restarted pc, and also shut down the pc.
6) Logged onto a different pc as myself and Lync 2010 opens for me. When another end-user log onto my pc, they duplicate the same issue with Lync stalling and not opening and receive the same error message.
7) Uninstalled and reinstalled Lync