Photoshop cs5 is not able to use the camera raw 8.6 plugin, only up to 6.7, which you already have.
If you need to open some non supprorted camera raw files into photoshop cs5, you could us the 8.6 dng converter to convert the files to dng copies, which cs5 should then open.
Adobe - Adobe Camera Raw and DNG Converter : For Macintosh : Adobe DNG Converter 8.6
how to use