Are you getting any error messages when saving? The reason I ask is that when I get an error 12, I just exit the game, go to my Saves file in the Electronic Arts directory in my My Docs folder, and delete my game - it's easy to spot because it will have been renamed with an extension that says
.bad. Bad file is bad. I delete it and that automatically creates a copy of the game from the back-up file. I just re-start and my game will be there. You might want to go take a look at your saves to see if you actually have .bad game files.
I've only experienced one instance of being unable to open a saved game, and that was with a custom world. I don't know what happened and I haven't attempted to use that world since, so I don't know for sure but it might have to do with creating the game and then installing HELS. Playing old saves after updating seems to be problematic for many people, but since you're creating new ones I don't know what's going on.
I can tell you though that I get a lot of crashing since installing HELS and the latest patches, plus various bugs and quirks that can be very irrating. In addition to the occasional error 12, I've recently experienced the basement/pool tool crashing problem, and yesterday I rotated through some created sims that I placed in my neighborhood and I experienced two instances of instant aging to elder status. In one case it was probably a delayed normal aging but in the other I know darn well that both sims were close in age and now one of them is an elder way before the other.
Anyway, I digress. I find that frequent saving helps. I try to save every 15 minutes or less. Also save often if you are adding items to the household or remodeling a lot. The game seems to have difficulty with trying to save a large number of changes all at once. Yesterday I lost an entire remodeled basement because the game crashed when trying to save it all at once. So for me at least, the crashing seems routine at this point. The game's a mess, and yet they're busy working on another EP.