EIDT: By “disable” you mean the off state right?

Just use the button’s name to set its state like this:

on init 
	declare ui_button $myButton
	declare ui_button $anotherButton
end on

on ui_control($anotherButton)
	$myButton := 0 {sets $myButton into the off state including the picture state}
	$myButton := 1 {sets $myButton into the on state including the picture state}
end on

In case you really meant disabling a button there is a new article now which explains buttons in detail and also shows various use cases (like toggles, disabled buttons or controlling multiple buttons at once):
various use cases for buttons

Have you put the correct text file into your pictures folder? The number of animations needs to be exactly 6 for a button (see instructions above)

Although I beleive this is not the actual problem here: did you keep the exact same distances from one button state to another with your button image? (see the example above) Kontakt devides the total height of your button image by 6 and thats the height of one button state then.

How do you trigger your button actually inside the note on? Maybe you wanna use a label with an overlayed transparent button instead? So that you have more control over the picture states. See this animation tutorial

EDIT : Sorry I totally got you wrong first .. the 108 (or 109 to be more precisely) should be fine. The image width is 108px so I actually don’t know why it gets cropped with your setup?!
Did you use another image file or resize this one?

I don’t know if this is a bug with Kontakt or if it has any purpose but yes, you may need to add one more pixel to your actual image size.
In this case it’s 108+1 or 32+1. The +1 was just used to point out this issue more clearly. Of course you can also do $BTN1_X := 109 and don’t need to do this extra addition.