L'erreur access violation se règle simplement en passant le jeu en mode administrateur comme dit dans le dernier patch note
IMPORTANT NOTICE:
Many reported bugs, related to random crashes (Access violation error, from several minutes of gameplay to hours) are most of times caused by Windows DEP settings. Active DEP may also lead to poor performance.
On newer Windows versions and updates, Microsoft disallow applications to add themselves in to DEP exception list.
This can be bypasses by running game once "As an administrator". to allow game to register app into DEP exceptions list.
To do this, go to Steam Cossacks3 folder, usually:
C:\Program Files\Steam\SteamApps\common\Cossacks 3\
Press right-click on cossacks.exe file and choose "Run as Administrator". This is needed only once.