@maggie-officer Is this your issue?
If not, please take a screenshot of the error and attach it to a post. If it is the same error, please try this workaround:
I take it you haven't installed Late Night yet (it comes with the Starter Pack), because it's associated with a different error. If you plan to install it, the above workaround won't be necessary, because LN isn't affected by that same error. Instead, you'll need to apply this workaround, but only for LN; High-End Loft Stuff is unaffected.
https://bluebellflora.com/sims-3-packs-not-showing-as-installed/
By the way, you can update to High Sierra or Mojave if you want, although doing so doesn't fix either of the above errors. Just download the installer you want and run it.
