Guys, OP last post is 12-12-2011.
This is related to manual payment. For more information, you can google: "How to redeem a promotion code".
Google tell you how to redeem the code inside AdWords Help Center.
This works fine if this is first time you are using adwords promotion code with your computer.
However, you can't run multiple accounts using this method alone. Delete cookies & flash cookies doesn't stop Google from detecting that you have multiple accounts.