Download the DivX converter and set it to the "Home Theater" setting. Convert your MP4, 3GP, AVI and whatever other video files using this setting and it'll work perfectly on the Sonic.
Thanks, it worked.
Like Snookie, I had one MP4 that worked, and yet no other MP4 worked.
Is this DivX format mentioned anywhere in the manual or MyLink literature? What really burns me is they don't even mention anything about file formats in the MyLink video instruction on youtube.