Okay. The fix is the same for both Vista and XP users, except the former must first carry out an extra stage.
Vista Users
Open the Command Prompt and type:
Press Return.
Type:
Press Return.
This will install a Telnet application which is optional in Vista, but it's already present on XP.
Vista and XP Users
From here on the instructions are the same for both operating systems.
Open the Command Prompt and type:
You will then be prompted to login to the modem with a username and password. The default is one of the following:
The second option worked for me.
Press Return after typing the username and again after the password.
Once you've logged in, you will be presented with the command line of your modem.
Type:
Press Return.
This will list connection bindings.
Look for a line that contains GAME and some port numbers. For example: GAME(UDP) udp 27010-27011
Type:
Press Return.
The port numbers in this command must match the numbers that are listed in your GAME port listing, similar to the example above.
And now you're done!