Problem with Radial Blur

I was following a tutorial:
< http://fdbgt.endless-anime.com/main.php?id=ps7tutorials/mind blast>

and i ran up against a problem when, after using the brush to draw some random shapes/lines and w/e, I tried to apply radial blur and it was greyed out-whats up with that?
And yes I did create a new layer prior to drawing anything

What version of Photoshop?

Your image might be too large to work with Radial Blur, or in an image mode it doesn't support.