The "Out of Memory" error in Cossacks 3 is a well-known issue often tied to the game's engine limitations in handling modern high-resolution textures or long-duration matches with high unit counts How to Fix the "Out of Memory" Error Lower Texture Quality The most effective fix is to go into Options > Graphics Texture Quality
The error occurs when the game’s internal memory allocation exceeds that 4GB limit, usually during: cossacks+3+out+of+memory+work