nlapiInsertLineItem is crashing my browser

I'm trying to write a script that will add a new line item to a sales order.

The problem is that every time I call nlapiInsertLineItem my browser will crash. I'm using Firefox 2.0.0.12 + Firebug.

This is the test code (Client Script), it triggers on the recalc event on a Sales Order form.

 function recalc(type)  {    if (type != 'item') {      return true;    }        var line = nlapiGetCurrentLineItemIndex('item');        try {      nlapiInsertLineItem('item', line);      // ...do various nlapiSetLineItemValue tasks...    } catch (err) {      alert(err.description);      return false;    }      return true;  } 

I've tried different values on the line parameter: same number as current line, current line + 1, and leaving it empty, but it will produce the same result (= crash).