Well, it should be supported according to this list
http://helpx.adobe.com/creative-suite/kb/camera-raw-plug-supported-cam eras.html
What is the exact message?
What is your exact version of Camera Raw?
HOWEVER, CR2 files from my 5D MARK II opens just fine.
What has that got to do with this?
You can always try the free DNG Converter.
But maybe the Camera Raw Forum would be a better place for the question.