Have you tried turning it off and on again?
I've been getting increasingly frustrated after installing Pets. AFT save didn't give me any problems but WAG froze time and time again. Then the new save for Sammy also froze during the night.
The worst day of all - trying to load WAG. First try, Disc verification fail. Have to try again. Finally loaded save, when I went to save I had an error 12. What I should have done is restart, what I did was quit to menu and reload. That's when I had a crash to desktop. Next try, Disc verification fail. I think I played all of 5 minutes that night.
Add to this the general frustration of having although the blogs have more readers than ever, my blogs are also getting fewer comments.
While installing Skyrim on the virtual PC on this Mac, I was doing heaps of other updates and restarted both the virtual PC and finally did a few Mac updates and restarted it.
Low and behold, WAG is working. It's gone nearly a full day with no freezing and no problems saving (I'm saving ever few Sim hours.)
I don't tend to restart the Mac much. The manual says just put it to sleep when not in use and that's what I do. But if I start having problems again, I think turning it off and on again is now *way* up on my to try list.
And if you've never watched the IT Crowd, just do it. Too funny for words.