I know it's not the display( s ) (I've tried it on several tvs).
I've done the usual: different cords, power cycling, disabling display detection on the 360. None fix the problem.
I actually called Microsoft. They were clueless, nobody had any idea what I was talking about. I told him to do a search of their forums. It is preventing people who use HDMI from watching Copy Once channels, Netflix, and HD-DVD.
Just thought I'd drop by here and see if anyone had any other tips to try.