Many users have reported getting a similar error in the past two days. It seems related to some URL changes and lack of smooth redirect from old to new URLs. Are you able to load the new "Hub" page at https://www.xfinity.com/hub/ And then you click the user-in-circle icon in the upper right corner of the page and get the sign-in form and link to check email at https://xfinityconnect.email.comcast.net/ Which step(s) lead to the error (Hub page, account panel, sign-in, email link)?