I'm having a similar problem. Was able to get into Raedric's Castle via the vines on the west side of the map. I went into the priest area, down into the dungeon. I killed the woman down there, then I went back up to the priest area via the kitchens. Now anytime I try to leave the castle (upper ramparts or Siege Platform) the screen transitions to the loading screen, then a black screen with movable cursor. After that it just sits there forever.