I have set up a simple server using Forge 10.13.2.1291. The server loads up fine with no errors.
I used the same Forge version (both on my Windows 8.1 laptop and on the same PC as the server) to install the client. I have forwarded the port and double/triple/quadruple checked the IP address. The client minecraft versions load fine, but when I try to connect to the server it says "java.net.ConnectException: Connection timed out: no further information:".