Well I'm able to directly download the mp4 file now so I can see that it's there. The player .swf is there, the video mp4 file is there... hummm.
When I direct download the mp4, it wants to open in QT and not Flash. So I'm wondering if you have a version of the Flash player that you are testing in that is different than the plugin version used by the Web browser. or, the file is infact a QT file and not palyable by the Flash player. I don't really know the answer... but you say you have tested on your local machine and it works... right?
About the only other thing would be to double check the path you have set in the player params (properties panel) to make sure you are correctly pointing to the video file.
Good luck!
Video Man