Open Server Ports
If you are not playing from localhost you may need to open some ports on your server.
netsh advfirewall firewall add rule name="L2J Login Server" dir=in action=allow protocol=TCP localport=2106
netsh advfirewall firewall add rule name="L2J Game Server" dir=in action=allow protocol=TCP localport=7777
Requires elevated command prompt (Run as Administrator...).
Only these ports are required to connect to the server as a player.