Ah, this explains it then. I had overlooked that you just assigned the fx_bump action, but without setting the two variables it requires (skill41 and skill42).

The way to set the bump shader is:

action set_bump()
{
my.skill41 = floatv(50);
my.skill42 = floatv(50);
fx_bump();
....
}

The values affect the shader ambient and diffuse component. You can play with the values in the shader viewer. They are the sliders below the shader selector in 0..100 range.