I just got the TWC box yesterday, and curiously enough, the technician (who hooked it up while my wife watched) used the component video connection instead of HDMI. The picture quality on my Sony Bravia was terrible and never registered higher than 480i.
I reconnected the SA 4250HDC ( Powered by Cisco ) using the HDMI, and changed the input source on my TV and the video came up fine, and reached 1080i on available sources. I had to manually change the audio setting on the box to use HDMI, but everything seemed to work ok.
I watched a program with my Daughter for about an hour, and when switching channels I got the now dreaded GS511_HDCP_DLG page.
I manipulated my TV, the Box, and the only thing that seemed to resolve it was to remove power from the cable box (unplug, shutting it off did nothing) and powering it back up, watching it boot and reload it's operating software, reconnect to TWC's head end, and negiotiate with my TV.
It works for a while, and then I shut the TV off, return and turn the TV on and get the GS511 page.
Calling TWC this morning to complain. My brother-in-law just got an HD box from TWC and received the 8300DVR I think, has not complained of this problem.
If Cisco did to Scientific Atlanta, what they did to Linksys, this problem should not be surprising.