I have the same problem with my ViP 722. According to a tech support person I spoke with at Dish, this is NOT a DVR or TV problem. It is a HBO/Cinemax problem, or rather, something that HBO and Cinemax are doing at their end, randomly and arbitrarily screwing things up with every distributor of their content.
Their position makes no sense to me. I am no expert on HDCP, but I seriously doubt that the method used by the 922 (or 722) to establish and maintain an HDCP encrypted connection over the HDMI interface is in any way controlled by content providers.
I have no doubt that the content providers can require (or not) an HDCP connection, this is apparent given that only HBO/Cinemax has this issue - but if the receiver is intermittently and erroneously detecting that a fully compliant display device is NOT compliant, this is clearly Dish's fault.
The fact that it works initially (or after you unplug and replug the HDMI cable) shows that the receiver can reliably establish this encrypted link in the first place - but something is later causing it to lose the link, and it never succeeds at re-establishing it. It seems to me that this is where the Dish (Echostar?) engineers should be focusing their effort.