On the Book of License, playing on Hard difficulty isn't that challenging if you set up the right strategy for developing your character, building your castle, and training units. Use your second hero to gather resources, with skills focused on resource gathering and building structures in your castle. There was a bug on the Book of License, but it was fixed in patch 1.2, I think. I fixed it by saving before the fortress appeared. I've been playing for 3 months on the Steam version, so I don't know if the bug will still be there.