Why doesn't my Sims 3 game on my Macbook update?

I have the original Sims 3 downloaded onto my Mac. I also have a few of their expansion packs including Late Night, Medieval, Ambitions, World Adventures, and Generations. all of them except Generations installed. Whenever I try to install Generations, it tells me that I have to update the Sims 3. So when I go to update it, it updates but in the middle it crashes and says an error occured and doesn't update. I'm going kill myself if it doesn't decide to work. So wtf is wrong with Sims 3? Or can it be my laptop? Either way, I need HELP.