Solved! Go to Solution.
There is a thread about this issue here: https://forums.xfinity.com/t5/Customer-Service/Can-t-manage-your-account-online-Getting-an-error/td-...
I've asked a Comcast employee to help you. You should expect a reply in this thread.
Hi, Jmpmanfan - I'd be happy to assist you with modifying your current services. Please send me a private message with your account information (full name, address, phone or account number). Click on my name ComcastElla, then click Private Message Me.