Ah, yes. If you looked around the forums a little bit more, you, like me, would have noticed that a large amount of players have complained about this bug. It's also widely discussed on the 'Official Bug List' thread (found here). Users claim to have found fixes for this, eg. clearing all other quests before attempting the quest or clearing your inventory before starting the quest. Whether there is any truth behind these 'fixes', I have no idea. Sorry you were so uninformed and I wish you the best of luck.
That worked comfirmed for me at least, gotta log out after deleting all quest and item in quest invent.