Division by zero when using vertex array

When I try rendering a terrain (from heightmap) using a vertex array, I get a floating-point division by zero whenever the z-coordinate passes a certain value. Rendering is fine when I use a simple brute-force approach. I made sure the generation of the vertex coordinates is correct, and when I move around the landscape not crossing that particular z-border, everything is rendered correctly as well. I also made sure there are no other divisions that could make a difference. Any ideas? ----------------------------- Jappie BabJap Productions "There''s no such things as bugs; they''re just unintentional extra features"