Setting a line item and doesnt work in IE 6.0

I have a custom form where I want to automatically add a line item to a transaction when the form loads. The strange thing is that the code below works in Firefox 1.5.0.7 but fails in 6.0.29 with an 'unknown exception'. I used the line item example in the documentation as a template.


function onFormInit()
{
  nlapiSelectNewLineItem('item');
  nlapiSetCurrentLineItemValue('item', 'custcol_processingfield', 'T');
  nlapiSetCurrentLineItemText('item', 'item', 'Project Expense : Meeting-Speaker Expense');    
  nlapiSetCurrentLineItemValue('item', 'custcol_paramvalue', '150.00');      
}

function doPostSourcing(type, fldname)
{
    if(type == 'item' && fldname == 'item')
    {         
        if(nlapiGetCurrentLineItemValue('item', 'custcol_processingfield') == 'T')
       {   
          var rate = nlapiGetCurrentLineItemValue('item', 'custcol_paramvalue');

          if(rate != null && rate != '')
          {
            nlapiSetCurrentLineItemValue('item', 'custcol_processingfield', 'F'); //turn the processing field off