I was getting the dreaded "Video Error" as well right after I installed my Ceton card. They had me try everything, install new Beta drivers, etc........I read somewhere that people were getting rid of this error by clicking off the navigation sounds in WMC. So, I did that, VOILA!!! I can watch Live TV no problem. But I wasn't going to accept my brand new HTPC to be crippled in not hearing the navigation sounds. I searched and searched online.......I found that some people have changed their audio from 5.1 to Stereo (when used as a regular desktop). I was messing around with the sound options through the control panel. I tried that and turned on my navigation sounds in WMC - NO VIDEO ERRORS!! I re-configured WMC to send a 5.1 signal to my receiver and I tested it. It worked! I tested SpikeTV (which doesn't transmit in 5.1) and my receiver changed to show only left front, right front, and sub working. I changed the channel to ESPN (which I know is a 5.1 signal), my receiver lit up with a 5.1 audio signal - ALL channels working. No Video Errors to speak of.
Just my 2 cents...............
Denon AVR-3311CI, Denon DVP-602CI, B&K Reference 200.7 S2, Belkin PF60
Sony BDP-S5000ES, Silverstone HTPC (6 Tuner DVR & 10 TB Media)
PSB Stratus Minis, PSB Stratus C6, PSB Alpha S surround, James Subwoofer EMB-1200
Sharp LC-70LE755U, Harmony 880 Remote