I found this on http://forum.ea.com/eaforum/posts/list/4345628.page and it worked perfectly:

After about 2 weeks trying and sending e-mails to EA Games they finally managed to make my pass code to work, This has been happening mostly for people that migrated their account to the countries which didn't existed before on Xbox Live (for instance Brasil, Colombia, Russia).

I use Xbox 360, and when I try to redeem my Pass Code it kept saying "unable to process online pass - try again later" but after EA investigations the only way to make it work, is to enter the code on your Xbox Marketplace and redeem the code there, you have to download a file that says "limited edition Need for Speed" the download is small, 108kb and it installs automatically, as soon as you download and install it, just launch the game, and the multiplayer will be available, as well the extra space to take pictures!