I realize that the thread is dead, but I just endured a very frustrating 50 minutes stuck in the same predicament, so I thought I'd give my two cents.

I'm not really sure of how I became unstuck, but keep in mind that you also need four ivory keys and a skeleton key to complete the level and open the western exit to cross the chasm. Use the ivory keys on the keyholes located by the four doors hiding the switches and then throw the switches behind said doors. Use the skeleton key on the keyhole in the West-bound hallway heading out of the Barrier. I think that the combination of clicked switches, turned skeleton key, and depressed pressure plates opens the exit on the West side of the Barrier. I know this is not very helpful, but if you (of whoever else is stuck) keep trying you should make it through the Barrier and across the chasm. After all every level is self contained and all the quest item and keys needed to complete it are located within it.

Question: I had it several times now that rolling boulders changed direction, blocking a corridor and forcing me to load an earlier save. I assumed that it might be connected to the cycles setting (which I changed according to your suggestion), so I changed it back to "auto", and I haven’t had the problem again since I did so. Is this just coincidence and the boulder issue is a normal bug within the game that sometimes occurs, or could these two things really be related?