I'm experiencing a problem in trying to update some billing information. I was trying to update some apps on my iPad and, as normal, iTunes asks for my Apple ID password. I enter it, but it then asks me to update my billing information. A window pops up, and it appears that the security code from my credit card is missing. I enter it, and it gives me an error saying it's invalid. I tried updating it through Apple.com, thinking the problem was on the iPad or something. Same issue. It won't let me update the security code from my credit card, and I can't update apps, purchase more, etc. Any help is greatly appreciated! Thanks!
EDIT: I've tried restarting the iPad, as well as syncing it with iTunes.
I had the same problem. Try to update your billing information via iTunes on Mac or PC. Even if it still won't remember your security code, you should be able to purchase what you want. I don't know why Apple Store has that problem, but it worked for me. :)