It's my first playthrough and I'm at Nature of the Beast. Now I helped the Grand Oak and returned his acorn by trading it from the Mad Hermit before I even encountered the barrier.
As I understand, either the Hermit or the Oak will help you if you side with them but I seem to be locked here. The Hermit says he will help me if I kill the Oak, but I can't talk to the Oak. It only greets me and I get no dialogue options. Also, it's not hostile so I can't attack it, so now I'm stuck. Is this a bug or is there another way of removing the barrier?