8 bit to 16 bit and back again

[dtscds]

I bought Kevin Kubota's Digital Boot Camp book. In there he talks about converting your image from 8 to 16 then back again. This is supposed to prevent "posterization" and make color transitions smoother.

He says to incorporate this as the last step in the PP process, right before you print or send it to be printed.
Here is his workflow:
Do all your pp work
Save as a "master" file with layers intact
When it comes time to print, convert from 8 bit to 16, flatten the image, then convert back to 8 bit.

Pretty easy to understand and follow. Until I tried to re-convert to 8 bit. It was 'grayed out' and I couldn't convert. I could convert up to 32 but that was the only option.
I closed and re-opened the file a couple of times but got the same results every time.
Any ideas what I am doing wrong?
I am using CS2 if that makes any difference.

[srdanz]

What mode is it in ? if it is e.g. in multichannel mode, it won't allow 8-bit images. Make sure you're in sRGB color space (or CMYK) to switch to 8-bit colors...

[johnastovall]

I can't understand why you would ever start in 8-bits unless you were shooting sRGB JPEG's.

Start in Raw with the ProPhoto color space and stay there until you have to go to 8-bits for an sRGB JPEG for the web.

Use the extra headroom that working in 16-bits gives you.