I also get a CTD when i finish a Alien Base Assault Mission. When i want to save i get CTD too, but i was lucky and i could save.
Here is the Download for the Save
i will now describe, how to reproduce the CTD, first you should eliminate the aliens that are left, it should be 2 Sebillians, after this, you will get a Window, that new Researches are available. if you close this, you will get a CTD.