The small elevator with the skull faces on it against the wall with green torches near the start of the level has disappeared. If I stand near the area, and press 'A' the sound of it activating will happen, but the actual block isn't there, it's basically invisible and I can walk right through it like it isn't there..

I have killed myself and restarted the level, and it isn't there, and I have reloaded the game and it's not there, and I have restarted the Xbox and booted up the game again and it's not there.

Please help, I'd like my achievement for completing Doom 2.