OK, in my situation we have two 722's connected to a DVDO Edge to the same HDTV. When trying to PPV a movie My 722 got the HDCP error message, but the other 722--set the same as the other--did not and authorized the purchase. This is the same movie at the same time. I always open the movies on all boxes to record to DVR so I have copies to finish watching if I can't finish within the first 24 hours at one box (this was the case, I had to finish at a 2nd DVR).
So, again the same HDTV, trying to PPV a movie at the same time on two different 722's connected to the same HDTV through a switch processor. One authorized the purchase, the other did not. Both running through DVDO Edge, but I checked the DVDO Edge and made certain that HDCP was ON for those ports. Also, identical HDMI cables (monoprice). I even rebooted the box with the HDCP error message and no change. All was the same for both boxes, there really is no reason one should have been able to purchase the PPV and not the other.
My point is that it isn't always the customer's TV, but, judging from the many posts on this board concerning very good brands of HDTV and my recent personal experience, I believe sometimes it is DISH's fault, as in the box isn't reading the data correctly and all is well with the HDTV.