js购物车问题，请高手帮忙！不知道是什么问题？郁闷了几天

我的能购物，但是有的商品能买，但是有的商品买不了，说什么已经加入到购物车中，请修改数量！代码如下：
//<--Start--从cookie中读出订单数据的函数
function ReadOrderForm(name) {
    var cookieString=document.cookie;
    if (cookieString == "") {
        return false;
    }
    else {
        var firstChar, lastChar;
        firstChar = cookieString.indexOf(name);
        if(firstChar != -1) {
            firstChar += name.length+1;
            lastChar = cookieString.indexOf(';', firstChar);
            if(lastChar == -1) lastChar=cookieString.length;
            return cookieString.substring(firstChar,lastChar);
        }
        else {
            return false;
        }
    }    
}
//-->End//<--Start--添加商品至购物车的函数
function SetOrderForm(item_no, item_name, item_amount, item_price) {
    var cookieString=document.cookie;

    if (cookieString.length >= 4000) {
        alert("您的订单已满n请结束此次订单操作后添加新订单！");
    }
    else if(isNaN(item_amount) || item_amount<1 || item_amount.indexOf('.')!=-1) {

        alert("数量输入错误！");
    }
    else {
        var mer_list=ReadOrderForm('24_OrderForm');
        var Then = new Date();
        Then.setTime(Then.getTime()+30*60*1000);
        var item_detail="|"+item_no+"&"+item_name+"&"+item_amount+"&"+item_price;

        if(mer_list==false) {
            document.cookie = "24_OrderForm="+escape(item_detail)+";expires=" + Then.toGMTString();
            alert("“"+item_name+"”n"+"已经加入您的订单！");
        }
        else {
            if (mer_list.indexOf(item_no) != -1) {
                alert('此商品您已添加n请进入订单修改数量！')
            }
            else {
                document.cookie = "24_OrderForm="+mer_list+escape(item_detail)+";expires=" + Then.toGMTString();
                alert("“"+item_name+"”n"+"已经加入您的订单！");
            }
        }
    }
}
//-->End//<--Start--订单修改更新cookie的函数
function updateCookie()
{
    var limit=document.OrderForm.elements.length-3;
    if (document.OrderForm.update.value=="修改订单")
    {
        document.OrderForm.update.value="更新订单";
        document.OrderForm.submit.disabled=true;
        //<--
        for (i=1;i<limit;i++)
        {
            document.OrderForm.elements[i].disabled=false;
            i=i+2;
            document.OrderForm.elements[i].disabled=false;
        }
        //-->
    }
    else{
        document.OrderForm.update.value="修改订单"
        document.OrderForm.submit.disabled=false;
        //<--
        for (i=1;i<limit;i++)
        {
            document.OrderForm.elements[i].disabled=true;
            i += 2;
            document.OrderForm.elements[i].disabled=true;
        }
        //-->
    var Then = new Date();
    Then.setTime(Then.getTime() + 30*60*1000);
    var values=document.OrderForm.storage.value
    document.cookie="24_OrderForm="+escape(values)+";expires=" + Then.toGMTString();
    }
}
//-->End//<--Start--删除单个商品的函数
function Delete(TableID,id)
{
    var confirm_delete = window.confirm("确定要删除吗？")
    if (confirm_delete)
    {
        var deletedList=document.OrderForm.storage.value;
        var broken_deletedList=deletedList.split("|");
        
        for (i=1;i<broken_deletedList.length;i++)
        {
            if(broken_deletedList[i].indexOf(id)!=-1) delete broken_deletedList[i];
        }
        
        var new_deletedList="";
        
        for (i=1;i<broken_deletedList.length;i++)
        {
            
            if (broken_deletedList[i]!=undefined) new_deletedList=new_deletedList+"|"+broken_deletedList[i];
            
        }
        
        document.OrderForm.storage.value=new_deletedList;
        TableID.deleteRow();
        updateTotal();
    }
}
//-->End//<--Start--更新价格总计的函数
function updateTotal()
{
    var new_total=0;
    var limit=document.OrderForm.elements.length-3;
    
    for (i=2;i<limit;i=i+3)
    {
        new_total=new_total*100+document.OrderForm.elements[i].value*100;
        new_total=new_total/100;
    }
    
    if(isNaN(new_total))
    {
        document.OrderForm.total.value="输入错误";
    }
    else
    {
        document.OrderForm.total.value=new_total;
    }
}
//-->End//<--Start--更新价格小计的函数
function updateSubTotal(m_id,new_amount,price)
{
    var price=price*100;
    var new_subtotal=new_amount*price/100;
    var n_m_id="id"+m_id;
    if(isNaN(new_amount)||new_amount<1||new_amount.indexOf('.')!=-1)
    {
        document.OrderForm.elements[n_m_id].value="输入错误";
    }
    else
    {
        document.OrderForm.elements[n_m_id].value=new_subtotal;
    }
    updateTotal();
}
//-->End//<--Start--更新storage的函数
function updateStorage(m_id,new_amount)
{
    if(isNaN(new_amount)||new_amount<1||new_amount.indexOf('.')!=-1)
    {
        alert("数量填写错误！")
        document.OrderForm.elements["aid"+m_id].focus();
        document.OrderForm.elements["aid"+m_id].select();
    }
    else
    {
        var the_list=document.OrderForm.storage.value;
        var single_list=the_list.split("|")
        
        for (i=1;i<single_list.length;i++)
        {
            if (single_list[i].indexOf(m_id)!=-1)
            {
                var old_single=single_list[i];
                var broken_single_list=single_list[i].split("&");
                broken_single_list[2]=new_amount;
                var new_single=broken_single_list[0]+"&"+broken_single_list[1]+"&"+broken_single_list[2]+"&"+broken_single_list[3];
                the_list=the_list.replace(old_single,new_single);
            }
        }
        document.OrderForm.storage.value = the_list;
    }
}
//-->End