z-values

[np1]

hello,
i ran into this weird problem:
i am extracting the z values from a heightfield surface , that i
subdivide with a uv pointgrid.
all the values remain 0 in the z axis although the z-orientation is
right. if i use a simple sphere it works perfectly.
if i use a simple surface that i distort -no problem. am i overlooking
something? i have done this before and it always worked.
thanks for your help
n