Unable to open a movie error message

I have QuickTime software installed on my Mac Os X 10.5 machine. There are a few .mp4 movie files which I am trying to view with my QuickTime software.
When I try to open the files with QuickTime it comes up with an error message
The movie could not be opened.
An invalid public movie atom was found in the movie.
I tried playing the same .mp4 file in Windows with QuickTime and it comes up with the same error message.
Is this format not supported or do I have some issue with the file itself?
