Problem with mod - End Turn freeze and crash

[Relentless Hunter 7]

As the title says, I have an annoying problem with that. Basically, I created a mini-mod in which I transfered everything from the faction of Persia in Alexander to vanilla and swapped Parthia with it. And I mean everything, from units, to names, to models/textures and colors, to symbols etc. Everything went smoothly, I was able to playtest enough battles while constantly checking out the imperial campaign and everything worked like a clock. At least up until the moment where I clicked to save my campaign game in turn 1. Then the game froze and I was thrown back to the desktop. Same thing happens when I am ending my turn. The moment when I click End turn the game freezes and throws me back. No CTDs or anything suspicious up until this point. So I can't save or advance the game.

Could you help me please?

[Relentless Hunter 7]

I should also add that my saved files somehow exist as .sav files after I save and the game CTDs. I just can't access them by loading them.

[Relentless Hunter 7]

Wait, that's it then? After 5 days and no one seems to know the answer with a problem of a 15 years old game? And on TWC of all places?
Wow....