Saves from the free version not being upwards compatible feels like a punch in the face to players who enjoyed the "demo" and decided to buy the latest release and DLCs. :/
We've talked about this more than once. The game will crash and pop up an error if you use old saves. Do players need bugs? No.
Therefore, we have found a solution. Use the "New Game +" mode to skip already completed quests in previous saves. Rewards are saved.