Caquina You won't be able to install the world through the launcher because of this issue:
Launcher crashes when I open the downloads tab in Sims 3 | EA Forums - 12167613
But trying to download it is a good test of whether the problem is still present, since you get exactly the same error when you try to download at the Main Menu. So you can test that way without having to open and close the game all the time. Once it's fixed, try the Main Menu again.
Did you recently change the email address or password associated with your EA account? Does either one have special characters? The launcher doesn't like those, so you'd need to remove them. Please also delete the file labeled [your email].bin inside Documents > Electronic Arts > The Sims 3 > Downloads, and clear Safari's cache and cookies. Finally, open Keychain Access, inside Applications > Utilities, search for sims3 , and delete any entries you find. Then try again to download the world.