Interesting occurance. Soloing this quest on my cleric, I purchased/summoned a hireling to assist me with the barrier puzzle. Upon completion of the quest, I attempted to recall and received the error message "You cannot go on raid adventures with hirelings in the party." I assume that the House Cannith explorer area is set up as a raid area and that is why I couldn't bring the hireling there. Fine, I attempt to boot the hireling... However I can't seem to do that either.
Luckily I had UMD/teleport scrolls... But the only other way I could think of would have been to log out and back in. Any thoughts on this? Bug? Or maybe I just don't know what I'm doing... Heh.