I've used Handbrake as recommended in this helpful thread (Put Videos on Droid) to convert .avi files to .mp4. I got a "Sorry, this video cannot be played" when I try to play it on my Droid. I also tried downloading an .mp4 file from a YouTube video (as converted by file2hd.com). But I still get that error message. I know this topic has come up before and it usually seems to be the way that the file was converted rather than some kind of setting on the Droid. What else should I try?