I can't calculate Convex hull of a point collection with a shape file.

[GangHan]

I have a point shape file in attachment. I want to calcute the convex hull polygon of the points in that file. But when I use the \ArcGIS\DeveloperKit\SamplesNET\Engine\GPConvexHullTool sample, I can't get the convex hull polygon. It  only return a blank shapefile. Why? The shape file is right in Arcmap or ArcCatalog. I use the arcgis 9.3.
Thank you.