Adobe Premiere 9 elements error

Hello,
I have the Premiere 9 elements on my Mac but I have a problem with all mp4 video types. When I try to open them there is always an error which I managed to get a screenshot of and is now attached below. If anyone has suggestions on this please help.

Unable to load movie
The selected file cannot be played because your system does not have the required compresser/Decompresser(Codec) installed.
