Hello Friends. I tried to buy a digital MP3 player on Amazon.com today and after I try to checkout from my shopping cart, I got struck there on the payment page. but in spite of selecting Amazon balance as payment option and having sufficient balance in my Amazon account ( from gift cards ) I was not able to click checkout button because it was disabled with a message "Please enter your payment information to continue" (Snapshot attached) I believe that credit card it totally optional. Where I am doing wrong? Can you please help !