PROBLEM SOLVED!! :thumbupboth:

Seems that Poser isn't in to imaginary numbers. :sneaky:
Some of the Square root nodes get inputs that "mathematically" are zero, but in practice there must be some rounding errors and it goes just a tad negative - enough to throw off a whole block of the surface.
So the fix is to check this (Clamp probably) before the square root.

Thanks for the help guys - I was really worried that there was some sort of limitation to using displacement, now I'm happy again.

Later, I'll post a new script including the fix and the simplification.

Rô

My favourite question is "Why?", my second favourite is "Why not?"