Hmmmm, now you've mentioned that Pescado, I wonder if the problem I'm having is down to removing AM. Most (not all!) of the plots in my town are gone. Not empty, I mean not even the plot exists. Instead, there are just holes in the world, with blue underneath. I haven't tried a new game yet (I was kidn of hoping not to, but maybe it would be for the best, seeing as I lost ALL my relationships. Again, I don't know if that's a WA or AM problem).
I just began having that issue as well. Is this in Sunset Valley? Did you use Delphy's tool that converts the Sims3Pack files into the .package format? It seemed that Riverview was somehow overlaid on top of my usual Sunset Valley, and all the lots were blue and see-through. I removed all the Sims3Pack -> .package files, installed Riverview through the launcher, and now it works just fine.