That is new impossible mod, no save game at all
Sry man ,have no idea what could be problem there. I had sometime bug when i try to save game, but it just freeze game and i go in windows and `kill` in manually, then start again and load most recent save. But to not be able to save at all, i never had that type of problem.
Try to find folder c:/documents/my documents/my games/kings bounty/$save and see if it exists, there should be all save files from game (at least in default installation), maybe something f...ed up that folder.