You can try these progams to see if they can help.

AVIcodec is a free multimedia file analyser for Windows which will tell you the codec required and where to download it.
http://avicodec.duby.info/

MediaInfo will do the same.
http://www.mediainfo.sourceforge.net

GSpot may be able to identify any problems with the MP4 file itself
http://www.gspot.headbands.com