I'm sure this is the response no one wants to hear, but I had to reinstall all of my games. Generations still doesn't work on my Mac, so I'm returning it, but all of the other expansion packs work still.
I also had that problem today this morning when i went to play on my mac book pro. But after i started to play the launcher again the game was fine. I think ea is doing something
Try reading the three threads mentioned in this one helpful thread. Your problems has been solved previously and a little reading will get your game running smoothly.
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http://forum.thesims3.com/jforum/posts/list/748338.page