I'm still having problem using the NN4 and a Canon 7D + 17-55 zoom and setting the position of the knob/camera holder on the upper arm.

When I change the zooming on the lens, I have to change the position along the arm: 17mm -> 75, 28mm -> 60 and so on.

When I unscrew the knob, it doesn't unscrew, instead it goes backward then eventually there's enough space to remove the holder from the guide on the upper arm. Only then, I can move it to the new position.

What am I doing wrong?