I can not save my game. I have an error window saying "Unable to save !". The automatic save is not working either. I have with the problem with both Zeus and Poseidon.

An idea of where the problem is coming from ?

Thanks for your help ! Playing Pharaoh waiting to solve the issue, not bad ^^

Did you install the game into program files? Then it could be a rights issue, since it tries to save in that place and might not be allowed to. Reinstall elsewhere, program files is not a good home for old game for this reason.

Great ! I have reinstalled the game on an other disk and it is working now.

Thank you for your help !

I had the same issue. Reason was synchronizing in-game profile with cloud, but this profile was created earlier on a different computer.
Game tries to create save game file in non-existing folder location. If you don't have it you can create it manually.

Save game file location:
<game_folder>\Save\<Profile_name>\

I didn't have <Profile_name> folder. The correct path for example for profile named "Test" and game installed od drive D:, should looks like:
D:\GOG Galaxy\Games\Zeus and Poseidon\Save\Test\

I hope this solution will be helpful :)