You can check to see if you can communicate over the port that is being used by the server.
For the Reprise NLO Server, the default ports are 2764 and 2765.
For the RLM CimLM NLO Server, the default port is 10106.
On the client you can use Windows PowerShell (For Windows 8/10) to see if the client can communicate over the port that is being used.
Open Windows PowerShell through the Start menu.
Use the command "test-netconnection IPAddress -port XXXXX"
Replace "IPAddress" with your server's IP Address
This will test to see if the client computer has access to communicate over the port. If it succeeds that means that the client is able to use that port.
If it fails, this means that something is blocking the client from communicating over that port. This could be anything from network permissions, security software, or router settings. You will need to figure out what is blocking this port and get it allow access.