Extension doesn't match file format?

I've run across a few of these with mpg video, can anyone tell me what this means? I can still play them in media player and VLC but not Qtime.

Thanks
Steelsheen

edit:changed the extension to wmv and I don't get message, how/why would the extension be changed, scan and bitzi OK's file

Quicktime has it's own format that it prefers to use.
That's why there are two major computer companies. Microsoft uses some file types and Apple uses a different type. Sometimes they are interchangeable just by modifying the extension at other times you've got to use quicktime or mediaplayer depending on which extension or file type they are using.