Entering the Hall of Echoes is suppose to be a one way trip; you shouldn't have been able to return to the battle tower, in human or dragon form.
AFAIK, from the walkthrough, etc, this should be the case. Actually trying the dragon stone myself, though (US Xbox release), I found I could return to the battle tower in the 2 dragon sections of the Hall of Echoes (no problems re-entering in dragon form), but not from either human section.
