HoF: Game does not unlock completed missions

[xencut]

As the title says, in Hammers of Fate although I successfully complete the missions, instead of moving to the next mission, it prompts me immediately in the main menu screen. After that, the already unlocked missions are locked again and I can only choose the first mission available by default. I can load the game from my last save (I can choose any save in fact,regardless the mission), but nevertheless the game does not proceed to the next mission. The only solution was to start over again the whole campaign progress starting from mission 1.1, but it comes to a point that it loses all progress. I searched around the forums, but didn't find any similar problem. I would love a solution.