Stuff bought with sim points not letting me install

So, some of it works, but some of it tells me to get the "latest update" on the sims to install it because the install failed. It doesn't say I need an expansion pack (usually accompanied by a little yellow triangle right next to it, saying that you don't have the expansion packs necessary) so I'm not sure what "update" it wants me to do, or even where to get it. I've done hours of searching to look for it, but as far as I can see, I have the latest update. Thoughts? 

Also, I'm KICKING myself for not buying the premium version of the supernatural pack, because i really want the "pea shooter" plant that comes with the premium version. But I'm not going to buy the whole pack again just to get it. (it helps ward off zombies from your garden)