Scriptable cart and checkout issue

Hello everyone.
Since Netsuite fixed the defect, i am now able to create external so invoice and cash sales and attach form level script to it.

I was following the BOGO sample script in help doc to add additional item to the cart when some item exists.

I am getting some serious set back here and keep getting Unexpected error or "Unable to add item to list" error.

Below is my code:
function onInit(type) {
return;
}

function onRecalc(type, action) {

}

//As instructed in BOGO sample, i attached onFieldChanged function to Field Changed handler.

function onFieldChanged(type, name, linenum){
addUsb('commit');