Lots of users recommend using DVD Catalyst. Note: I'm not connected to them in any way.
I think they have a $10 Software that will convert DVDs for you. Try that. Based on what users are saying, it works great.
That is what I use. After talking with tech support from the makers of that app, seems it might me the memory card, as the movies play fine off the internal memory.
Anyone have trouble playing off the SD cards?