A lot of gamers have had problems unlocking the Dragon Tower via the Dragon Snare quests.

To unlock it, you need to get four stars on one of the chapter three scenes. The difficulty is that the scene required is different for every player. The best thing is to work your way through them and it should unlock.

Some users have reported the quest not opening up even after fulfilling the above, in which case you should contact Playdom and raise a support ticket.