NAT Filtering on Thomson 585 v7

[#1]

My daughter has just rang to say she is having problems with Modern Warfare 3 when she gets a message 'Attempt to join games failed as NAT too strict.'
Not being a gamer I am stumped and hope someone here can help.
The instructions with the game say: Ensure under security option annymouse NAT redirection is allowed and not filtered. It may also be refered as Filter Internet NAT redirect.
Could anyone please explain what this means and how to ensure this in the v7 - if possible.
Cheers.

[#2]

Ok, A bit more searching a I found a couple of threads relating to this issue and will work through the advice there and report back if the problems persist
MW3 taking ages to find a game
Simple Strict NAT Type Cure !!!