Lens blur greyed out

[TLicense]

Hello all,

I'm pretty much a complete newbie to PS and I'd like to do some tilt shift editing.
The problem is that the lens blur option is greyed out. Can anyone tell me how I can get around this?
I can use all the blur options apart from the lens, radial and smart blurs.

For reference I'm using Photoshop CS (version 8).

Many thanks!

Tony

 

[TLicense]

Figured it out....

The image I was editing was a RAW image from my Canon EOS 300D, which is 16 bit. I converted it to 8 bit, and all was good!