I have one user who is having issues connecting to the Lync server from outside our network. When connected to VPN and/or directly plugged into the network, the user doesn't experience the issue. I logged into the same computer and was successfully able to connect to the Lync server from outside our network.
The specific error is, "The server is not responding or cannot be reached. Sign-in may be delayed while we retry the connection..."
What could be the problem?