There have been a few with this problem. Not sure what the fix is and I kind of remember having this problem last year when I joined and was buying a phone besides. I can't quite remember how I was able to fix it but kind of remembering emptying out the cart and trying again. If that doesn't work try it again but before putting your order back into your cart try deleting your cache and/or browser history and then try again. I kind of remember it took me 2 or 3 tries and it finally accepted payment.
