Recently, several enabled Remote call control (RCC) users reported that they were having issues making phone calls from Communicator.
When they attempted to call a number, they got a “Cannot locate <user>” error message and when they clicked on Retry, they got another error message, “There may be an error in the address. Check the address and then try again.”
After some troubleshooting, we found out our CSTA Gateway server was using an expired certificate.
For communication to take place, the CSTA Gateway and Microsoft Office Communications Server 2007 R2 must exchange signed server certificates each time a TLS session is opened.
After installing a valid certificate and restarting the services on the CSTA Gateway server, our users were able to make phone calls from Communicator again.