By default the webGUI (for security reasons) only allows access from the local system, not others on the network.
I know that there is a setting to disable this security default. It is noted in one of the webGUI development threads. I'm afraid I don't recall exactly what it is. I checked the documentation but I know there is still some stuff missing there. Do a little searching and you should find it
Other than this you must of course also allow the port to be open on the computers LAN firewall, or you will not be able to each the server anyway.