function AddAdditionalProductToCart(merchantProductID, quantity) {
    wsCall = new wsObj();
    wsCall.functionName = "AddItemToCart";
    wsCall.callbackFunction = AddItemToCartResponse;
    wsCall.addParam("MerchantProductID", merchantProductID);
    wsCall.addParam("AttributeStr", "");
    wsCall.addParam("Qty", quantity);
    wsCall.addParam("ShopperID", shopperID);
    wsCall.addParam("MerchantID", merchantID);
    wsCall.addParam("ImageIDs", "");
    wsCall.sendRequest();    
}

function AddItemToCartResponse() {
    if(wsCall.goodResponse()) {
        var dom = wsCall.http.responseXML;
        var crMessage = dom.getElementsByTagName("AddItemToCartResult")[0].firstChild.nodeValue;
        if(crMessage.substring(0,5) == "ERROR") {
            //Show the error message.
            alert(crMessage);
        } else {
            document.form1.submit();            
        }
    }
}