Actually, on NG the GUI port is 18190 and you should start by making sure that your firewall is listening on this port (use 'netstat -an' to check for TCP port 18190 in LISTEN mode).
Then unload your policy (you should unplug the external interface first to be safe) using the NG command 'fw unloadlocal'.
Now connect your GUI client and make sure that your policy includes the right services in the first rule for admin.
Alternatively, and perhaps more correctly, simply install a good SSH client (I prefer Vandyke SecureCRT, but PuTTY is pretty good now) and port forward port 18190. Connect to the firewall on port 22 (SSH) and then run the GUI to connect to localhost (127.0.0.1). Hey Presto, a secure tunnelled GUI connection *and* you dont need to mess around with the GUI-Clients files.
shaggerTM
(Fascist Security Consultant and all-round nice guy).