... and if libdvdcss2 wasn't (on the core and MD) don't forget the other packages. (w32codecs or w64codecs (on 710 64 bit) and the other I can'y remember of the top of my head but the wizard asks if you want all three. They have to be selected and are checked when loaded.
810 doesn't yet- at least on mine. Unlike 710, you cannot select those from the list during the setup and have them installed, you have to to it manually. There is another post about logging into a MD as the root- I wonder if he/she was trying to install the software directly on the MD rather than go through the core. I ran into this myself and eventually just went the /usr/pluto/diskless/moon ## way to get done on the MDs what I needed done from the core.
BTW- even if libdvdcss2 is installed on the core, it must be installed on the MD that you want to watch an encrypted DVD on. That is to say, that if you installed libdvdcss2 on the core, but not a MD, and put a DVD in the MD's DVD player you will get a similar response to what you (speedyone) experienced- the screen would blip black for a moment and then kick back to the main screen. Usually (maybe every time) a message is displayed in the upper left hand corner stating that the dvd is unreadable or something isn't installed. FWIW.