I have a saved game that reliably crashes after a minute or two.  It appears to be triggered by one of my constructors that's trying to build a starbase: two enemy vessels are harassing it, and when it creates the starbase, they momentarily get "shoved" into the planet, at which point the game crashes.  I wonder if that could be the problem?  Unfortunately it doesn't seem to be possible to upload files on this forum, but maybe that's enough information for you to reproduce it...

(edit)  It has nothing to do with the enemy ships: I can create the starbase while they're on the other side of the gravity well, before they get anywhere near the constructor, and the game still crashes right after the starbase appears.  It just doesn't like that constructor for some reason.

(edit 2)  If I build some missile turrets and scare off the enemy ships, *then* I can build a starbase.  This confuses me: I've built other starbases while enemy ships were around (even while the constructor was being attacked), but there does seem to be a connection between the presence of the enemies and the crash whenever I try to construct a base.