I have just purchased The Sims 3 Ambitions Expansion Pack and once I downloaded it and try to run it..the window pops up saying there was an error during start up please see log for more details. But you can't go anywhere once that window is up? It just allows you to push ok and it closes it down
Have you tried uninstalling Sims 3 (don't delete your saved games), then re-install, update to latest patch, then install Ambitions? Sorry, I don't play the game so I can't offer any specific help, which is why I recommended contacting EA support.