Recently I had problems with a house I wanted to download from a sims3pak that would download but wouldn't show up in my game. After a bit of snooping I found the solution here. I tried it out and it worked just fine for me.
Also I know some people prefer using packages over sims3paks and the way to turn the second into the first is on that page as well.
Hopefully this will help anyone looking for an alternate route to getting a stubborn house into their game.