I have the same problem. I went into worldbuilder and managed to track down the cause to Victoria. If I delete all her cities, the game continues. However, I'm not able to find out what exactly is causing the error. I tried deleting all cities which where not on her main continent, and the error persisted. Then I tried deleting all the cities on the main continent, leaving all the other cities, and the error persisted. I also tried saving a worldbuilder file to edit in wordpad, where I replaced all UNITAI_COUNTER with UNITAI_DEFENSE. Still the same problem.
I'm using BTS v 3.00, no patch at all. I'm scared I won't be able to load old saved games after patching.
If one of you guys has the time to check out the attached saved game and find a solution, that would be amazing. I was really enjoying this game...