Btw, here's a quick example I just did for you with a sphere, ground plane (a cube actually) and a spotlight. I left the raytracing defaults in render globals and in the spotlight's attributes, it's setup like this:

no decay
cone angle 40
penumbra 10
dropoff: 0


raytraced shadows on:

Light radius: 2.009
shadow rays: 10
depth limit: 1

You should experiment with lower values....increasing radius or rays will slow your rendering, even for simple scene such as the one I did.