I've asked a Comcast employee to help you. You should expect a reply in this thread.
Hello sjgthompson. We apologize about the error message while trying to navigate to this portion of our website. While we work to resolve this error, I can assist with reviewing your account and modem upgrade options with you. To get started, please send me a private message and include your full name, service address, and account number so I can access your account.