There is a bug with online bill pay, i have experienced it in firefox on linux and windows.
I have two cards that I split the bill with. The first time I experienced this bug, I paid with card #1, and it processed just fine. Then I tried to pay with card #2, and it said the payment could not be processed. I checked with my bank, and they said that the reason it did not go through was because the wrong security code was being entered. I double, triple, quadruple checked: I was entering the right security code. The payment with card #2 would not go through even when my account was accessed from a different computer, with different settings (same browser though.) I was not experiencing issues through any other services from any other companies and I was able to pay with the automated phone service, so this is a sprint website specific problem.
The second time I experienced this, I paid with card #2 first, and that went through fine, then tried paying with card #1 and got the same error. At this point, if I had to guess, paying with multiple cards for a particular billing cycle results in sprint producing the first card's security code for any subsequent payments, even though they might be with different cards that use different security codes.
Are the payments the same amount? I know this will cause an issue.
I use a debit card on one of my bills and the same account on another but I use the bank id and account number. The money comes out of the same account just using two different methods. If one of the payment methods you are using is debiting a bank account you may try using the bank account info instead.
Just a thought
Larry ~ OKIESTRO