asp.net 中增删改查Remove问题

private void Add()
    {
        int i = 0;
        string sitename = this.TextBox1.Text;        IISManager iis = new IISManager();
        iis.Connect();
        iis.WebSiteId(sitename, ref i);        DirectoryEntry site = new DirectoryEntry(String.Format("IIS://localhost/W3SVC/{0}", i));
        PropertyValueCollection serverBindings = null;
        serverBindings = site.Properties["ServerBindings"];
        String binding = String.Format("{0}:{1}:{2}", _ip, _WebSite, _Port);
        if (!serverBindings.Contains(binding))
        {
            serverBindings.Add(binding);
            site.CommitChanges();
            Response.Write("添加成功");
        }
        else
        {
            Response.Write("<script>alert('已存在!')</script>");
        }
        
    }
    private void Del()
    {
        //id = Request.QueryString["id"];
        int i = 0;
        string sitename = this.TextBox1.Text;        IISManager iis = new IISManager();
        iis.Connect();
        iis.WebSiteId(sitename, ref i);        DirectoryEntry site = new DirectoryEntry(String.Format("IIS://localhost/W3SVC/{0}", i));
        PropertyValueCollection serverBindings = null;
        serverBindings = site.Properties["ServerBindings"];
        String binding = String.Format("{0}:{1}:{2}", _ip, _WebSite, _Port);
        serverBindings.Remove(binding);
        //serverBindings.Remove(Convert.ToInt32(binding));
        //serverBindings.RemoveAt(Convert.ToInt32(binding));
        Response.Write("删除成功");
    }protected void Button2_Click1(object sender, EventArgs e)
    {
        _ip = this.TextBox2.Text;
        _WebSite = this.TextBox3.Text;
        _Port = this.TextBox4.Text;
        Add();
    }
    protected void Button3_Click(object sender, EventArgs e)
    {
        _ip = this.TextBox2.Text;
        _WebSite = this.TextBox3.Text;
        _Port = this.TextBox4.Text;
        Del();
    }
在这里，我用增加方法，能够增加数据，而同样用类似的方法来写删除，为什么能执行到 Response.Write("删除成功");
 serverBindings.Remove(binding);也执行了，什么都不报错，就是删除不掉数据