The step that says you should select "None" (and then press the "Done" button) is where I get the "Your request is temporary unable to be processed" popup in the iTunes store. I also can't change my billing information anywhere in the Apple ecosystem - iTunes app on my Mac, Apple's various websites, System Preferances. I spent 1-1.2 hours with two Apple support people on the phone today and they could not figure out what was going own. The iTunes support specialist told me he didn't see anything wrong with my account. I can't purchase anything from the iTunes store, I can't purchase additional iCloud storage, I can't change my payment information (even to a different credit card).
The guys on the phone suggested I go into an Apple Sore and have a Genius help me.
Any other ideas? The AppleID I'm using is one I created almost 5 years ago and has only ever been used to MobileMe and iCloud syncing, I have a gmail AppleID that I use for iTunes store purchases.