I can't open .CR2 files in Photoshop CS4

I'm unable to get the .CR2 files from my new Canon Rebel T3i to open in Photoshop CS4.  I just got this camera and I never had this problem with my old camera (Rebel Xsi).  The raw files from the Xsi will still open, but not the ones from the new camera.  Can anyone help me understand why this is happening?

Thanks,   Jo