Button Icons don't show.

The function below creates a working button but It doesn't display the Icons.
Where am I going wrong?
 
function forwardButSetUp(pg) {
var pgRect = this.getPageBox("Crop", pg);
var fldRect = [];
fldRect [0] = pgRect[0] + 700;
fldRect [1] = pgRect[0] + 70;
fldRect [2] = pgRect[0] + 760;
fldRect [3] = pgRect[0] + 10;
var f=this.addField( "nextPg","button",pg, fldRect);
loadIcons();
f.buttonSetIcon("fwdUp","0");
f.buttonSetIcon("fwdActive","1");
f.buttonSetIcon("fwdOver","2");
f.buttonPosition=position.iconOnly;
f.buttonScaleHow=scaleHow.proportional;
f.display = display.visible;
f.buttonScaleWhen = scaleWhen.always;
f.setAction("MouseUp", "this.pageNum++");
}