Where did you get those particular files from?
One of the issues with MP4 format is in the fact that MP4 is a container format.
Thus, MP4 files can be differently decoded, and some devices do not support all decoding variations. More info
You might have go as far as converting those MP4 files into a different variation of MP4.
I could recommend a free program for converting MP4 and many other video files. Here is a direct link
to XviD4PSP 6, because their website winnydows.com
requires Silverlight and does not open in some browsers.
It has PRESET configurations for various APPLE devices, Sony, Toshiba, Youtube, etc.