[Current Issue] Sims 3 "serious error" when loading save

saracraft234​  I've merged your post with the master thread for the "serious error" issue.  Please see the first post for help.

For the worlds not being installed, if you're referring to the InstalledWorlds folder in Documents > Electronic Arts > The Sims 3, this would only contain worlds you installed through the launcher, as in, Store or custom worlds.  Sunset Valley and the worlds that come with expansions are stored in the game's program files.