Sims 3 Game Won’t Save?

So I’ve been playing the Sims 3 and created a family and town, etc. on one slot and it saved fine. Then, my sister created her own Sims family on a different slot, but her’s won’t save. And, I’m trying to exit her’s so I can play on mine, but I need to save hers first, but everytime I try to save it, it says, “An unexpected error has occurred while saving: Error Code 12. Please consult the readme for details”.
So I looked at the readme, and all it said for error 12 was, that it’s a world save file failure.
Any ideas on how I can save the game on my sister’s Sims, so that I can exit it and play on mine?
Answer #1
we got that error on my computer i found that it is because of low disk space also the reloaded version does it