I'm trying to register my game on Orgin but it keeps saying my code is invalid

Have you already dowloded this game?

Yes, I have downloaded it

I'm having the exact same problem. I'm trying to register my base game (so I can get extra stuff :D) but it keeps saying the code is invalid. My game is store bought (so not a digital download) and a couple of years old. Does anyone have any idea how to get it to register? 

See instructions here: http://answers.ea.com/t5/The-Sims-3/Information-How-to-Register-The-Sims-3/td-p/387162/

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