dark brotherhood quest help, yet again i fail to do something alone Options

[MarkII]

howdy. im on the dark brotherhood quest where you stage that guy in chorrol's death and then revive him a day later in the chapel undercroft. or, should i say, you would if you could get in there.

my problem is that the undercroft needs a key, and when i pickpocket the key from the one person in the chapel with it, nothing happens. ive got the key, i can see it in my inventory. it says "chorrol chapel undercroft key". so i mosey on over to the undercroft door and try to open it. it tells me that the door requires a key to open.

hmm....

i tried the unlcok cheat as a last resort as well but it wouldnt work. any suggestions?