Trouble using OCS due to server connectivity

We would like to use OCS for our organization since CA certifications were already expired. So we have to renew it again. But we are already having troubles on using OCS. When people try to exchange messages to other people within the organization, a warning message appears. Together with the symbol “!,” the message goes like this; “Some calls to and from people outside of your corporate network may not connect due to server connectivity problems.  Try signing out and back in, contact an admin…” One more thing, a person said that it can’t totally access the Office Communicator at all on his laptop. An error message like this occurred; “Cannot Sign in because the server is temporarily unavailable. If the problem persists, contact your system administrator.” Right now, we are using OCS Server, Conferencing Edge and a Communicator Web. I would like to ask for assistance to unravel this problem. I’m not yet familiarize on the functions and features of this software but you can give me instructions on it. I’m good at following instructions.