What LAN Problem? Also fix your title.. Online first then title then date.. Also take MLG Off. We know your going to use those setting but gamers doing searches are going to come here and attract more out of towners. Just state in the paragraph that your using MLG/Gamebattles settings.
the main problem is that MW2, on LAN, has no pregame lobby meaning players can only join the game mid-match and you are unable to gather players and set up the game in a pregame lobby. there is 1 host that can set up the map and gametype in a lobby, but the other players cannot join the room until the match has already started, which would be very difficult to organize at a large-scale event.
on top of this, there are the system link rank and unlockables issues. the way it works in MW2 is, you have separate ranks for online and system link, so if you're ranked 70 online, you have to completely restart and do it all over on system link, meaning MLG would have to get 600+ profiles to 70 which isn't very reasonable.
so, as of now, the only way to play the game at tournaments is to be hooked up to a live internet connection, like cod4. mlg wouldn't be able to do this for 120+ teams and 480+ xboxes, so unless the game is fixed it will once again be an online-only title.
however, i'm sure MLG is trying really hard to get in contact with IW and to get a patch to fix all these issues, but they did the same thing in CoD4 and over a 2 year period, nothing was fixed. so it all just depends if IW takes the time to create a patch to fix all these issues or not.
From MLGpro.com