I'm sure I'm missing something but I am getting an error when trying to add items to the shopping cart using the new SSP API.

Here's a sample of the code I'm using:

 ...  function service(request, response) {   var order = nlapiGetWebContainer().getShoppingSession().getOrder();   var itemInfo = {    internalid: request.getParameter("internalid"),    quantity: parseInt(request.getParameter("quantity"))   };     ...       nlapiLogExecution("DEBUG", "Add to Cart", "Attempting to add item with id "+itemInfo.internalid+" with quantity "+itemInfo.quantity+" to cart.");         try { order.addItem( itemInfo ); }   catch (ex) {    /*     ALWAYS THROWS AN ERROR. THE ERROR IS:    JavaException: com.netledger.app.site.scripting.store.exception.NLStoreScriptFailedOperationException: Failed when adding item to cart    */   }    }