You know, I may have an idea of what it was. I'm gonna try to explain in full detail. Maybe someone can learn from it.
So I'm trying to get 1,000 in my garage so I put my gamesave in a flash drive and took it to a friends house. We bought over 200 cars on his PS3 without the update. So i came back to my house and copied the save and now I can't view the cars that I bought at his house only the ones from my own PS3.
Weird, I know. But its probably the reason.
SlyckTiresSony don't seem to like people using the same account on more than 1 live PS3, so it comes as no surprise that the process isn't all that well supported.