It seems when you start the quest, Anska's Scroll you must complete the quest the first time you are within the cave. You cannot leave the cave and come back another time. The Dragon Priest that you fight will not respond, and killing him is the only way to open the two gates on either side of him. First time only, I figured this out the hard way and had to kill Anska to fail the quest and get it out of my journal. Speaking of killing Anska she can be killed so don't go wandering off to far into the dungeon without her, she might die considering she wears almost no armor.