Cannot load saved game

I have a game that's been ongoing for many turns. Recently, I could not load the save game, the game crashed and went back to Steam. I managed to open the file by starting a new game, then immediately chose Load Saved Game. That worked for a while, but now I cannot do that either. I have verified files etc. I suspect it has to do with size of the game, as I can start new games with no issues. Anyone know of a way to get it to load, or do I need a new computer ...