problem about photoshop CS2

I think your file is change to 64 bit colour, you must change back to 32bit,
It is in the end of the same row of "change CMYK/RGB"

JPEG only support grayscale/RGB/CMYK mode. If your photo is not using this mode or it has multiple layers, then you cannot save it as JPEG. You have to change the mode back to grayscale/RGB/CMYK or flatten image to a single layer, then you can save as JPEG format.