This guide is for those who only have the Sims 3 Base Game installed. For help with the same error message on Macs with additional Expansion and Stuff Packs installed please go here.
There is no 100% fix for the Unknown Error messages countless Mac users experience with Sims 3 as it can be for many different reasons. There are however a few things you can try to fix it. The following are known to cause the error to pop up when only the base game is installed:
- When uninstalling ALWAYS do a complete uninstall, never just use the Uninstaller as it leaves files behind which can cause the Unknown Error message after a subsequent reinstall. Full instructions on properly uninstalling here.
- Purge RAM before launching the game.
- If your Mac is a 2013 or later model, check your graphics card/chip is supported and add the details to the game files if necessary.
- Go into Documents > Electronic Arts and move the Sims 3 folder to your desktop then try launching the game again. The error could be caused by a corrupted save or incompatible CC/Mods or downloads from the Exchange.