@lisaagt Any packs downloaded through Origin will be fine for mac OS, so don't worry about that part. The unknown error is to be expected on a mac, and there are several steps you might need to take to fix it. After you've seen my reply, I'm also going to move this thread to the dedicated Sims/mac section, where you'll get help specific to mac OS.
Since you've already uninstalled and reinstalled, it's a good idea to start with a clean uninstall. If you don't remove TS3's hidden library files, you may not be able to launch the game going forward.
https://bluebellflora.com/how-to-do-a-clean-uninstall-and-reinstall-on-a-mac/
Once you've done so, you can follow Bluebellflora's guide to installing TS3 on a mac. If you get past the unknown error only to see a connection error instead, you can either ignore it and just start installing your packs—the problem will go away once you install any pack that isn't World Adventures or High-End Loft Stuff—or you can fix it this way:
https://answers.ea.com/t5/The-Sims-Mac/Sims-3-quot-There-is-a-problem-connecting-to-the-server-quot/...
If get stuck on any step or have questions, please post back, and we'll help you through the process.
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I don't work for EA. I'm just trying to help fellow players with their games.
