Vizard does not have a "shadow" feature. The problem is that the avatar material is not using ideal values. Try the following in your script:
Code:
avatar.color(1,1,1)
avatar.ambient(0.6,0.6,0.6)
avatar.emissive(0,0,0)
avatar.specular(0,0,0)
These are the values the default avatars use.