the credit you entered is invalid while changing app store country I have 3 credit cards, AMEX VISA and Master, all of them are assuringly valid in Japan, but when I tried to switch country back to Japan, it always said "the card you entered is invalid." whichever I used.   I don't have any unpaid bills or else, just changed the country to update some apps not displayed in Japan's app store.
Anyone can give me an explanation or how can I get out of this?  

Thanks in advance.
The credit card used must be issued in the country of the app store, in your case Japan. It's not enough to have the card accepted in the country (most cards are accepted globally).