I'm in chapter 7, Highway 17, at the part where you have to go under the bridge to disable the forcefield. BUT when I open the door to actually get under the bridge the game loads, and then the screen fades to black. I can still see my health, armor, and ammo, but it is like i feel off a cliff. After a few seconds the game loads again and im back in front of the door; where i last saved the game. Can anyone explain if its a problem with the disc or what?