unable to open raw photos from canon eos 5d mark II on photoshop cs4
Support for the 5D Mark II began in Camera Raw 5.2
Photoshop CS4 shipped with Camera Raw 5.0.
Download and install Camera Raw 5.7 (the last version of Camera Raw which was compatible with CS4)
Photoshop CS4 supports Adobe Camera Raw 5.0 to 5.7.
What is the current version of Camera Raw Plugin installed on machine?
it should be 5.2 and later because Canon 5D Mark II start supported since relase of Camera Raw 5.2.
For more info please refer following article:
Camera Raw plug-in | Supported cameras
Camera Raw-compatible Adobe applications