Not Right Kind of Document?

I just got Lightroom 2 and upgraded to Photoshop CS4. When I select a picture in Lightroom to edit in CS4, Photoshop says "Could not complete your request because it is not the right kind of document." The file is a raw CR2 file from a Canon 50D. Lightroom reads the file just fine but not Photoshop. Help?

More info. Lightroom is using Camera Raw 4.6 while PS CS4 is using Camera Raw 5.0.0.178. Could this be the problem?

Problem solved with Camera Raw 5.2 update.