I downloaded the extra levels on Xbox Live. I'm attempting ton complete the (Kola Cel?) mission. It involves a submarine and a compressor room.

Anyway, I have been in the compressor room, disabled whatever it was, and eliminated all of the guards. At the bottom of the stairs, according to the many walkthroughs I have read, I am supposed to go through the plastic strips and outside. However, I cannot go outside. There is an invisible wall. It seems to be some sort of glitch. I cannot save and if I turn off the Xbox I will have to start over at the compressor room. Any ideas?