I've had this happen more than once. Those large houses just have too much stuff in them! It's hard for the game to process the lots that really are just overloaded. The houses are pretty, but they aren't very functional for actually playing the game. The best I can suggest is that you clean up your computer and game files, defrag and all that, restart your computer and game, then just try again. However, even if you manage to get these lots loaded, they probably won't play well for the same reasons they didn't load well.