Your payment method is not valid in this Store. Frustrating, isn’t it? This is the error AppStore users around the world are getting when trying to buy an app and they are requested a verification on the credit card.
Furthermore, users who need to change their payment method can’t do it and then can’t go back to the old one.
I can personally confirm this has been going on for at least 12 hours, while Apple is still mum on the matter. Well, their focus is most probably on the iPad 3, but if this thing continues until tomorrow, I suspect the event might not turn as spectacular for Apple.
Anyway, the Apple forums are full of angry users from lots of different countries. Some report they still can buy apps, but those who were requested a verification or a payment method change are practically screwed.
However this pans out, just don’t break your iDevices, we guess there’s nothing left to do than wait and hope everything will be back to normal tomorrow. One official post on the matter could have been nice though, but I guess this is just not the Apple way of handling things.