I also had this problem yet found a solution from Adobe themselves http://kb2.adobe.com/cps/404/kb404610.html When you attempt to import XDCAM EX clips or MP4 files into Adobe Premiere Pro CS3, you receive the error message "Unsupported format or damaged file." "For MP4 files that give this error message, rename the file extension from MP4 to MPG or M4V. This will invoke an alternate import module that will correctly handle the file." Hope it helps!
... View more