Error using nlapiGetRecordId on Item Receipt.

Hi
I'm trying to create a popup to warn the user that inspection is required of the items prior to accepting receipt.


The code im using is below;


function validateInspectionOfItem(){

var recId = nlapiGetRecordId();
var record = nlapiLoadRecord('itemreceipt', recId);
var numberOfItems = record.getLineItemCount('item');

for (var i=1; i <= numberOfItems; i++)
{
var inspectionneeded = record.getLineItemValue('item', 'custcolcustcol_inspection_needed', i);
var inspectionconfirmed = record.getLineItemValue('item', 'custcolcustcol_inspection_confirmed', i);
}
if (inspectionconfirmed == null && inspectionneeded == 'T')
{
alert('Please check the items and tick the Inspection Confirmed Checkbox.');
}
}

and the error being thrown is

Environment: SandBox
Date & Time: 3/4/2013 2:25 pm
Record Type: Item Receipt