I have CableVision who provided me with their set-top box and I've connected it via HDMI to my Onkyo A/V and marked input as CBL/SAT HDMI. I switch on my cable or A/V first (whichever - doesn't matter as effect is the same) and then when I'm selecting CBL/SAT (or already selected) ... boom: msg appears on my TV stating my monitor (in this case my A/V) doesn't support HDCP or whatever I should switch to component, etc. etc.
At this point, what I end up doing is in my A/V keep switching the HDMI inputs, go back to CBL/SAT and finally after sometime somehow magically the msg disappears and TV starts. Many times the video's there but no sound. Here again I have to go back & forth repeatedly. Switching off and on either the cable or the A/V doesn't help.
It's worthwhile to mention here although cable box is connected to my A/V via HDMI, I am still forced to use the cable line from my cable box to my TV for video as my A/V can't seem to down convert the HDMI input into a composite video output from my A/V to TV (input video) at all!