Nature of the Beast - Bug?

I am trying to start the "Nature of the Beast"-quest, but after I've talked to Zathrian, the Brecilian forest won't unlock and I can't enter the forest and finish the quest. I have played this quest with another character without any problems and I don't know why the area won't unlock this time. I've tried exiting the area and come back again, I've reloaded with different party-members and different dialogue options, but nothing seems to work. And when I go back to my first character and reload to a save before I started "Nature of the Beast", the same thing happens, the area won't unlock. It's really annoying because (as far as I know) you can't finish the game without doing this quest, and I really want to be able to do all the quests. Anyone got any suggestions to how I can solve this? I play on ps3 if that makes any difference.