SrfGrid question

Hi,

back in 2004 I wrote a script to make a 3D surface based on iso-elevation curves in the XY-plane. It was too slow to be useful but I could never shake the idea off me...

I'm now trying to do the same in Grasshopper and, 2 days into the project, I have a grid of 3D points that I'm trying to turn into a 3D surface. I'm trying to feed the points into the SrfGrid component but get an error message saying "The UCount value is not valid for this amount of points."

As shown in the attached picture, I have a regular rectangular grid op points, 15 in the X-direction, and 10 in the Y-direction. I tried putting both the #X and #Y into the U-entry of the SrfGrid component without results. I put a slider on the set to verify that the points follow in a logical direction in the list - in the picture, the slider is at 35 and the 36th point in the zero-based list is selected...

What am I doing wrong?

cheers,

wim