I have the same problem with not being able to get Monte Vista or Hidden Springs to load. Incidentally I also bought at least one of them from Walmart, but I'm pretty sure we would have heard if Walmart got a bad batch of videogame discs.
I'm pretty sure that part of the problem is that they are worlds as opposed to EP's or stuff packs. The reason I say that is I had Supernatural, Seasons, Town life stuff and High end loft stuff that loaded ok on the same day as the others and without any PC changes in between. Only the two worlds did not load properly.
I checked to see if they showed up in the launcher as downloaded content where I I have Barnacle Bay and Riverview. Those two work in game but they were bought a long time ago. FYI, I bought Barnacle Bay as a store bought disc and it is in my game just fine and Riverview is an online download .So that means that the game is obtained is probably not the issue.
I wonder if anyone else that is trying to load these worlds has forgotten to take out their custom content like I did. I'm going to try that next.