Well, this problem might occurs when there's an error with name files (such as launching a campaign with a faction whose leader got an invalid name, or if a rebel sub faction army is led by a general/captain with an invalid name).

It could also be that there's not enough provinces on your campaign map, which would lead to random CTD if you scroll over given areas of the map (in this case, the area around the capital of the faction would cause a CTD right after the loading).

And I guess it could be a lot of other reasons, wether I forgot them or haven't encountered them yet.