I'm on build 430. I tried to play an mp4... it dropped straight back to live channel. Then I tried an .avi and the picture played with no sound. Then I tried a DVD .iso file with no problems. I went back to the mp4 and the avi files, and now they played successfully. I also tried .ts (normal recording), .mts and .m2ts and they all played okay.
As per my signature, I have a Vu+Duo.
cheers