I have a few answers. First is, are you at a war with another country, and second is, did you fight a civil war? Both of these can cause the game to bug, and think you're still at war with that country even if they capitulate. There's unfortunately no way to reverse this (Except maybe blowing up the entire earth) So what I just do is save after every major decision so I can just reload if it bugs. I hope this helped :D