This is the biggest Mac/Sims 3 issue at the moment, apart from the unsupported graphics cards issue which EA STILL haven’t fixed after nearly 4 years…
The Unknown Error is a magical mix of Late Night and/or Ambitions trying to be installed onto a Mac running macOS 10.11 El Capitan or 10.12 Sierra. It’s that simple. We have a thread running over at AHQ where people are posting about it and yesterday a rather super person called coreylamalva414 posted a solution which appears to actually work (go and show him some love if it works for you 💚). His instructions can be found here. Good luck!
Edit – coreylamalva414 has uploaded a very helpful video to walk you through the fix:
I’ve set up a couple of pages dedicated to Mac specific bugs for both Sims 3 and Sims 4. They will of course be eternal works in progress and regularly updated. If you have anything to add that I may have missed feel free to leave a comment.
I’m not sure if this is a Mac specific issue so I’m just throwing it out there.
If you are trying to download University Life for the Sims 3 but can’t because Origin is telling you it hasn’t yet been released, please post in this thread over at EA’s Answers HQ. It seems to be an issue with the latest update – 220.127.116.1163 – 398079.
It doesn’t seem to be operating system related. but the more info EA get the better so they can (hopefully) fix it.