"change_tune is not Allowed in this callback type" but the script is fine!

The error message you're seeing is due to the fact that change_tune is not allowed to be used within the on note callback in KSP.

Your logic seems to be to randomly play one of three notes when a key is pressed: the actual note, the note above, or the note below. For the latter two, you're attempting to compensate for the change in pitch with change_tune, but since this function isn't allowed in the on note callback, you'll have to approach this problem differently.

Instead of adjusting the pitch with change_tune, you can prepare your samples in advance so they match the desired pitches, allowing you to simply trigger the corresponding sample directly. If this is not feasible, you might consider using other methods such as adjusting the group tuning in real-time or employing other real-time pitch manipulation techniques compatible with your Kontakt version.

However, if the core of your goal is simply to play neighboring notes in a round-robin fashion, you don't need to adjust tuning at all. You can use the play_note function alone to trigger the notes.

Here's an example that should work:

on init
   declare $RandResult
end on

on note
   ignore_event($EVENT_ID)

   $RandResult := random(1,3)

   select ($RandResult)
       case 1
           play_note($EVENT_NOTE, $EVENT_VELOCITY, 0, -1)
       case 2
           play_note($EVENT_NOTE + 1, $EVENT_VELOCITY, 0, -1)
       case 3
           play_note($EVENT_NOTE - 1, $EVENT_VELOCITY, 0, -1)
   end select
end on