[Update: Konami has informed fans via Twitter that the problem is resolved, but some people are still reporting issues. Contact Konami with your concerns if you are still encountering errors. I can confirm that my code finally works after the notification.]
Many users across the net (myself included) are reporting issues with their codes, and some have gone as far as to reach out to Konami and Microsoft to find out what the deal is.
Right now, Microsoft has confirmed that these codes are valid, they just haven't "activated" the system yet, and to wait 24-48 hours from today to try again. So basically, just sit tight, as they are working on it.
For the record, I was able to redeem my Gray Fox code on the PS3 instantly.