Weird Portal Problem

[lisalover1]

I was playing Portal on The Orange Box on my Xbox 360, and I encountered a VERY stange error. I was in the last testchamber of the game, and had to get to a certain area. I got to that area, but it was a dead end. At the time, I thought there was another way, so I checked a video guide online. That's when it got weird. In the online walkthrough, it shows the exact same corridor, but with no wall. The player didn't do anything different, but there was no wall. Here's the video: http://www.portalwalkthroughs.com/walkt ... 19+normal/

Around 4:15, you can clearly see that the corridor leads to another room. It doesn't do this in my game. There's a wall where the room entrance is supposed to be. I checked the video, and did everything exactly the same as shown, but it's still there. Has anyone else had this problem?

[DuManchu]

I ran into the same problem only with Half-Life 2. Ended up being a dirty disc.

You may also try going back one or two save points and reloading. That has fixed this issue for me before as well (before I realized the disc was dirty).