Things I bought in the Marketplace won't work.

I bought worlds in the marketplace. After downloading and playing in them, they would not let me create another world. When going to create a new world using the world I bought, it says downloading were create should be. I have played in all these worlds at least once. I would like to have access to these worlds again if possible. It doesn't matter the creator of the worlds, for it affects all creators. Thank you!