@Metalchairo , you’re a life saver.
Basically the suggestion is to restore the AI files to “factory settings”.
Unfortunately, after the last update my game began to show this error and AI does not play… I tried the above mentioned advice but it did not work… 
Same issue here now. I’ve reported the bug and, while it doesn’t get fixed, I’ll just have to play against the HD AI.
Are you using any mods? I got the bug fixed by removing one of the mods, more precisely the Forgotten HD mod.
If anyone is having this issue, disable the Forgotten HD mod. I went through my entire list of mods and disabling that one fixed the issue.