I need some help with the Krypt. I tried finding information on this elsewhere, but came up with nothing.

The first time I explored through the Krypt, I got to the dragon door, solved the puzzle, and went through. Every subsequent time I've gone to the Krypt, the door puzzle has been in the solved state but it is still closed and I cannot pass through it. The levers are also nonresponsive. I get the feeling that there is something obvious I'm missing, but I can't figure out what it is. Can someone help me out here?