MPEG-2 for QuickTime 10.0?

I get the error: "The movie is not in a format that QuickTime Player understands." when I double click on the .mpg file. Get Info show this file to be a: "MPEG-2 Video, MPEG Layer 2" file.

I am using Snow Leopard with all the latest updates. The version of QuickTime is 10.0.

Thank you very much for your help.
Olaf