So I've reached the part in the You Know My Name mission where you take over the sniper nest and you're supposed to cover Reed. But the thing won't fire. It keeps saying "firing mode disabled". I watched a YouTube video and there's supposed to be a robotic voice saying "new user detected" etc, and I don't get that. I go straight to Reed coming out of the door and then everyone immediately attack him and I can't fire or do anything, or exit the sniper nest. I reloaded the mission all the way back to the beginning, but the bug remains. Basically this has broken my game.