ok basically yoiur 360 preloads the maps to the HDD for easier loading. you may have a destroyed disc and still be able to play halo if you experiance any trouble loading maps. try loading a matchmaking gametype as the new update whipped the HDD so i needs to preload the maps again. if this doesnt work try lending a freinds disk loading a eahc map from his disk then playing each for a few mins if this contiues stop being cheap and buy halo2 again its like £7