You may want to take a look through the Bug forum to see if they have anything to do with save game crashes, if they do then there maybe a work around where you can edit the save and continue to play.
Also there are actually two autosave files, autosave and autosaveold I think.
So the oldone may still load for you, you could try to play past the point where the game crashes by playing another nation, then switch back. That sometimes works.
Or you could try a manual save every couple of days to try and pinpoint where the problem occurs.