Yea, its weird. I get through the AT onto level 4. I believe there is a giant skull bones, jaws or something just as you get there. Tane can not move outside the perimeter of those bones, therefore, can't proceed. He can return up to level 3 no problem though. I've tried everything, pointing, using keyboard, backing through, dropping items and then picking them up, changing his size to tiny, rebooting, without spells, stripped down to his undergarments (this one was just for fun), and no change.
Not a big deal if its just Tane, but thought it might be a problem for others. Different races perhaps? *shrugs*