Clouds only work in 8 bit, not 16 bit - too much hog on memory or some such thing (I asked Adobe once long ago). One thing that a lot of people forget is that they have After Effects or Photoshop Lightroom and those do not have the clouds filter. There was something called Photoshop Essentials, I think, something like that, which had a bunch of stuff in it but not everything and the clouds was one of the missing things. Also, make sure that you're not in bitmap mode, you have to be in grayscale, rgb, cmyk, or lab.