Halo 2 problem - near end of game. Glitch or stupidity?

So I just got an Xbox 360 specifically to play through the Halo campaigns. I'm playing Halo 2 and I'm on level 15: The Great Journey, sublevel: Delusions and Granduer, playing as the Arbitar. Right at the beginning of this sublevel, after Sgt. Johnson blows the door open using the scarab, you go in and take out the half dozen or so brutes. Ok, good - done. Now I know the door on the right is SUPPOSED to be open, but in my game, it's not. I reloaded from the last checkpoint and played again, I've even replayed the entire level in case it was a one time-glitch. But that door is _never_ open. So I can't proceed. I know it's supposed to be open because I've even watched a damn walkthrough on youtube: https://www.youtube.com/watch?v=uXB7ZtM8QeI At 8:15, there is the door, open after the Arbiter kills the brutes. What is wrong with my game? Am I being stupid and there is something else I was supposed to do for that door to be open?? What is the problem?? Thanks.

Well, I'm glad to know it wasn't just me, but apparently is some kind of glitch in the game. http://forum.teamxbox.com/showthread.php?t=337020 I had to replay the level 3 times before that stupid door opened, but at least I can now move on and finish the game.