If none of your limb texture files look like that, I'd start by removing your entire Cache directory. Maybe you have some corrupted cache files. If that doesn't do it....
Have you cleared all the Diffuse, Gloss, Specular, and Normal maps for your limbs and added them back one at a time? If so, does one of them in particular give you that weird sandy effect? That might help you narrow down if one of your texture files is incorrect. Also look at your texture files manually with an image viewer, just to verify they look like you'd expect them to. Perhaps you have your files named incorrectly (swapped the D,S,G,N for an incorrect one), so you're placing them in the wrong texture spots?
Or, maybe you have a corrupted scene. If you haven't tried it already, start a brand new empty scene, add a person atom, and then modify the limb textures on that new person. If the problem still occurs, and all your texture files look correct, and you cleared your Cache directory, we might need more information to determine what's going on.
Let us know...
