Ensure your graphics drivers are up to date. For recurring issues, performing a "Clean Installation" of drivers is recommended. Check Game Source:
If the above solutions do not work, you can try the following advanced solutions: cossacks 3 out of memory
Windows (all versions), primarily 64‑bit systems running the 32‑bit game binary. Ensure your graphics drivers are up to date
Frequent background writing can lead to memory leaks or corruption during long matches. cossacks 3 out of memory