Unable to claim Caer Bronach (bug?)

I'm playing through the Crestwood questline Still Waters and I've come to the part where I have to reclaim Caer Bronach in order to access the dam controls.  In my first playthrough, I was able to claim the keep and progress, however, in this time, the quest seems bugged.  I've cleared all the bandits on the lower levels, but when I get to the upper level to confront the final boss and claim the keep, nothing happens.  No boss emerges from the claim point like it should, and I can't access the area (receiving the message "cannot open from this side").  Is there a workaround or a way to force the quest to complete via the console? I recently attempted to claim the keep with another character, but ran into the same problem.