I just got off the phone with Scientific Atlanta. They confirmed that 4250HD is not compatible with HDMI 1.3 and above.

I got a brand new 4250HD box from Cablevision and I connected it to my Sony XBR4 via a new HDMI 1.3a cable. I didn't get any picture. I went through a troubleshooting session with a Cablevision support person who had me reboot the box. Still there was no picture. The explorer screen didn't show...