No game disc found, please insert the Sims 3 game disc before proceeding

I know this is an old thread, but I thought I'd stick my head in to say that downloading the game from Origin does NOT guarantee you won't see this error. I downloaded the game last night, along with a couple of expansions. It looked as thought the installations went through without a hitch, but first the game tried to get me to insert the Late Night disc over and over - I uninstalled Late Night, and the error switched to the High End Loft disc. After finally uninstalling THAT expansion, the error switched to the base Sims 3 disc, and now I'm stymied. I've never owned a disc for any of these programs.