Select server and Conn.Failed

Connection Failed message means your server is off-line.

Okay, so if your server is running (not crashed) and your client is still failing to connect, either it is trying to access the wrong IP, or there is a network block between your client PC and the Server PC.

Never mix and match 127.0.0.1 (localhost) and LAN IPs, and never mix and match LAN and WAN IPs. Which is to say, if your server is configured to recognise it's self on it's WAN IP, then connect the client via the WAN IP as well... and the same with localhost vs. LAN.

Check your firewall (Software or Router based) is not interfering with the connection. Ports need to be known and open for TCP send and receive and in some cases UDP as well.

If you are using Quantumfusion client, remember that "Server1" line in your "ptreg.rgx" and in your registry is ignored, and the IP in the exe is used instead.

I cannot be more specific without knowing which server, and client files you are using, and how you network between the client and the server.

Which is to say, you can set up on a virtual network across virtual machines, you can run client and server on the same machine without virtualisation, you can work via a LAN either over a Hub, crossed Ethernet or Router, or you can work remotely over the internet. Each option requires some slight configuration differences.