Well, I just discovered that MVA Blueray that I bought on Ebay doesn't work on my ps3. At first I thought I might have been ripped off, but after finding this thread, I realized the problem.
Fortunately I always backup my Bluerays, so I have the AnyDVD HD program which strips the digital protections and I simply made a copy of it. It works perfectly! and as a bonus, it gets rid of all the government warnings and additional useless extras that are usually on these discs.
If you're not used to doing this, there is a bit of a learning curve, but lots of good info here on AVS, and on the Slysoft forums which make the Anydvd software.