Team Ninja is aware that Ninja Gaiden III's online pass has been giving people trouble and has provided a notice on their Facebook page:
We are aware of the issue with the Online Pass for Ninja Gaiden 3 and are working to resolve the issue. For those of you with the PlayStation 3 version of the game, the online pass will be redeemable by 4pm Pacific time. For those of you with the Xbox 360 version, we are currently working with Microsoft to resolve the issue and we will keep you updated. Thank you for your patience as we work to resolve this matter.
Luckily, the Xbox 360 version has been working as of about an hour ago:
For those of you with the Xbox 360 version of Ninja Gaiden 3, please re-enter your code the online pass is now working.
Until the PS3 version is fixed, our own review for Ninja Gaiden III will be delayed until our reviewer Eddy Fettig has actually had time with the multiplayer.