I think the first thing you would have to illiminate is the HDMI cable. A HDCP problem does sound the most likely and this could be down to a poor quality / faulty cable.
Thanks, that'll be my first thing to try; a couple of replies in the other thread seem to point at this as well. I'll be annoyed if it is the cable though, it's a Profigold jobbie. I might just say sod HDMI and get a component switcher instead, then I can use component for HD and DVD.