Some games require a loading trick. Load your Ultimate Cheats/Codes disc and select cheats in the usual way. At the final screen (where you are asked to insert your game disc a and press `X` to play) swap the Ultimate Cheats/Codes disc for your game disc then press and hold L1 and L2 on your PS2 controller (the left shoulder buttons) - with these buttons still held down, press `X` to start the game. Keep L1 and L2 held down for a few more seconds until some game images appear on screen. You should find that any games in which you were experiencing difficulties will now load.