My friend has need for speed underground 2 installed on 2 laptops

When trying to play over lan he encounters a problem
THe problem is on one of the laptops it connects to the server hosting the game but when going to lobby it dont work it says connection has been lost.

I went over there today and tried it
I turnt off the firewall then tried it and it all worked then i turned firewall back on and it didnt work so i done it again and turnt it off and now all of a sudden it dont work when last time i done that it worked

The laptops are wireless
One is running windows vista the other windows 7

What is the problem?