Shortcut to move on Z-axis doesn't work

Hi! I’ve seen some people asking the same question, and I’ve tried all the suggestions on the answers… and it just doesn’t work! Actually, it works once, and then never again (which is odd).
The thing is: I’m taking an Udemy online course on Toon Boom, and the instructor is using Toon Boom Harmony 16. I’m using Toon Boom Harmony 17 (I’m not sure if it’s related). I’m right in the first steps of the course. He is teaching the basic shortcuts. All right. He shows us how to draw a simple ball and then a rectangle and when he teaches us the shortcut to bring the ball forward or back (alt+pgup/pgdn)… it doesn’t work for me. If I insist a lot, after many failed attempts, it works once. And then I try again on a different frame…nope. Many times, using ‘alt’ seems to be the shortcut for the ‘File’ tab (it often opens when I’m trying the shortcut).
Once again, I’ve seen the aswers given to other people for this questions and I have:

  1. made sure the camera is the part focused when I try to use the shortcut (the red line is there… I can see it!)
  2. The transformation tool is selected, the object is selected (both in the timeline and in the camera… but, once again, the camera is selected when I use the shortcut, that’s not the problem).
  3. The drawings are in "separate layers"in the timeline.
  4. I’ve read somewhere that, if you used the cutter tool, the software may understand the drawing is a bitmap. I’ve used the cutter tool on the ball at first (it’s a basketball), so I tested the shortcut with another ball, without using the cutter… it doesn’t work either.
  5. The shortcut preferences are on “Toon Boom Harmony” instead of “Studio” (someone recommended this).
  6. I’ve tested with other keyboards… doesn’t work.
    What am I doing wrong? Is there any other way to do this that is not the shortcut? I can’t find this option anywhere else.

Hi Laionilustra,
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Thanks and good luck!