Just upgraded from 3gs to 4s two weeks ago. Since then I cannot download apps on the phone, even free ones. When I select one and put in my PW it says "Before you can make purchases, you must tap Continue to sign in, then verify your payment info. So I go to the 'Account' page and everything is there and correct except my Security Code. So I enter that and instead of loading I get 'Security code is invalid.' I double and triple-check the code and all other info, and still get the same message. I also tried entering a different card- different number, different code. Same deal. What am I doing wrong?