Game crashes: questions and answers.

I decided to replay the campaigns of Heroes 5, downloaded the Gold Edition with all 3 expansions. The first campaign went fine, but in HOF, I encountered either a bug or something else. On the 3rd mission of the 1st campaign, the game crashes constantly, and on the same day, I can't load a save. When I click the "load" button (in the main menu), it crashes to the desktop, ending the game. I've tried running other people's campaign saves, and it's the same... I don't understand what to do to solve this problem.