Ouch, that error message doesn't sound good. I'm assuming this came up from sprint.com. Have you tried using a different brower or computer. You can always dial *3 from your Sprint phone to pay your bill over the phone. Here are other options to pay the bill as well:
Let me know if you need any further assistance.
Sprint Social Care
Sprint is proud to have been named to The Civic 50, an annual survey of America?s most community-minded companies.