AI not doing anything

[seadog]

A few turns into the campaign the AI stops doing anything and behaves as if it were unactivated.

I actually played quite a few turns without realising!

One time, when I was saving the game, a message box appeared saying something like: "the AI is not attached and there are no active players selected. Would you like to attach the AI?"

After I clicked the tick, the AI was active once again, which was a very noticeable contrast to the previous turns in terms of AI movement and attack.

Is there a way to trigger the above message box in the console/forcing the game to attach the AI?

[seadog]

Additionally, at the start of a new Polish campaign I started I got a message saying something like: the save file could not be accessed due to system restriction. This message appeared when I tried to end the first turn or save the turn.
I then had to load that save (still on the first turn) and it worked fine from then, but the AI only acted on the first turn. The next turns, it did not nothing, did not attack etc.

[Durk]

My guess from the second post, you are not running the game in administrative mod.
The first I do not know. Never seen AI shut off.