Can't have Feneris as a companion. Killed all the guys in the abandoned house, found the chest and it won't open. I am a rogue, not a problem but the quest marker just sits there, chest won't open and therefore can't complete the quest and get Feneris. Makes me SOOOOOOOO mad! My husband, playing on the same PS3 just a different profile didn't have that problem...he had other glitches
This happened to me once so i reloaded the autosave( upon entering the mansion) fought the enemy in the room at the end where the Shade creature w/ the key is. Immediately upon killing him i looted his corpse and got the Magistrate's key. My first time i failed to get the key bec. i waited too long to loot the thing w/c is a glitch. So i got it while his corpse was still visible and glowing (note that while looting him there still is fighting going on). But at least this way you'll get it.