I edited the title of this thread to include "Gray Ovals", so hopefully someone will see exactly what you're getting and have information.
Yeah, it's not a good idea to leave the game running for long periods of time. Our technical experts suggest restarting it every two or three hours because things get clogged up and restarting will reset some of the things than can cause problems.
Also, have you looked at the actual files on your computer to see if they are bad? If you're on a Window operating system, you need to go into My Documents/Electronic Arts/Sims 3/Saves. This will show you every save file you have in your game, plus the backups the game generates. If you see anything that has "bad" in the name of the file, then it's a corrupted file and needs to be deleted because the corruption can actually spread to your other save files. It's heartbreaking sometimes, but we end up completely losing save files sometimes.