If it's a new issue or you haven't played before, it's probably just that the Gallery is down. It goes down a lot and just starts working again later, seemingly whenever it feels like it.
If you've been having an issue consistently for days or more, make sure you're playing Sims in online mode. I'm sorry, I don't remember how you do that, but there's two places that have to be set to allow online access, one for Origin and one specifically for the Sims. If you've had problems since downloading the game or Origin, one of these may be your problem, and if so, maybe you can find someone who remembers/knows how to fix it. I had problems with mine, but it was a long time ago.
