This is almost always related to not allowing certain TCP ports between client and server. For Campus 4.x and 5.0, you must allow TCP ports 1683, 1684, and 8088 between your client and server. Make sure you can telnet to those ports on the server from your client. You should get a connection with no data returned. If you get a timeout or connection refused, then you need to work with your firewall/network team to open those ports.