Can't get ground shadow of my character with environmental lighting

I’m attempting to use a background for my character animation scene. I’m using Blender internal engine v 2.7. I have three lamps in the scene. If I don’t use them (even with the environmental lighting), the character has a flat look to him. But my question now is how to get the character to cast his shadow on the ground plane. I’m using a plane with shadows only for material. I’ve tried using seveal hdri and jpg images, but I still can’t get a ground shadow from my character. Can someone tell me what I am doing wrong?

Blend file:

the image textures are not packed in your file.