One idea - are any vertics actual attached to the bone? You can place a bone without binding it in med. You may have done so.
another test -
ent_bonerotate(my,"bone",vector(0,5*time_step,0));
You should see movement!
I am pretty sure I attached the vertices to the bones. When I open up the model in MED and press the Animate button, I am able to manually make the model bend forward and backward at the waist by manually rotating the waist bone.
Also, I tried out your test. Same result.
