Clear a Icon Javascript

I've tried this script that I found on the
forum, but can not get it to work.

I use another button that set up to clear the button and both buttonis set to “Icon
only”

var oIconClear =getField("buttonClear").buttonGetIcon({nFace: 0}); 

getField("Button3").buttonSetIcon({oIcon:oIconClear, nFace: 0}); 

Anybody who have an idea why it does not work