Yes, I have that problem with all Media Videos since May. Have not been able to watch any of those videos. Have not found a solution, yet.
I can not sign into NBCOlympics.com
I do not even find any place to sign in on that site; I also don't see a need to sign in.
Can you explain in detail what you are trying to to, and what happens when you try?
P.S. what is your operating system and web browser?
From the Comcast.net site, I sign in and go to the LiveExtra option. The first page has a LiveExtra Sign In - Watch Live the Olympic Games window box. The window box say 1 Sign In, 2 Watch and there is a radio box indicating Comcast or there is a drop down box listing every cable provider in the US. After selecting either of the options to select my cable provider the window box goes away, the view returns to LiveExtra. After a few seconds the view blacks out and the window box returns requesting sign in. It is a loop. I can't get out of it. I have removed my firewall, removed my security protection. Had two chat sessions with Comcast. Supposedly Comcast technitions have been working on this for 4 days. Nothing.