Adding Items to Cart Validation

I am working on writing a scriptable cart script. It currently does (or is suppose to do) 2 things, it won't let you add a specific item to the cart and it won't let you add something that is already in the cart to the cart. Here is the script:

 function customValidateLine(type)  {     if (type != 'item')   {    return true;   }        var itemId = nlapiGetCurrentLineItemValue('item','item');     if (itemId == "302"){           return false;   }      var qty = parseInt(nlapiGetCurrentLineItemValue('item','quantity'));   if (qty > 1){    return false;   }     return true;  } 

Currently the qty part of script works. It returns an error saying line validation failed. Item 302 is still allowed to be added to the cart.