Hmm, not sure but try this instead.

my.skill20+=1*time_step;
ent_animate(my,"Leg_STAIR_UP",cycle(my.skill20,0,100),ANM_CYCLE);

And let us know how it goes. If it make ANY difference...

"There is no fate but what WE make." - CEO Cyberdyne Systems Corp.
A8.30.5 Commercial