I've been playing this for a while, and right now I'm on the mission in the Frontier to stop messengers. I quit it at first, after several attempts, to play another game. I came there the next day, but when I cross the river, a GUI comes up in the middle, and the entire game freezes up. I wiped the disc, but it is still doing it, and I want to make sure it is not a problem with the disc/game. Please help! Thank you in advance!