Transferring purchased digital DVD copy to iPod

I recently purchased a DVD (Juno) with a redeemable code to download a digital copy for use with an iPod. I followed the instructions, redeemed the code, and was able to download it into iTunes. However, when I try to sync it to my iPod (30G 5th generation), I am told that I'm not authorized to play it on my computer. What's going on, and how can I get the copy I bought to sync?