I have completed the game and I am having the same problem.  I even tried a different hero and it didn't lock...but I have like 50 hours on my character and I need HELP!!!

I have a similar issue, except mine is with Bower Lake.  I can enter the Heroes Cave, but nothing else in Bower Lake.  VERY FRUSTRATING!!!!   I think the issue is the Slave Trader Quest. Someone please help!!!!