我的下载功能不能下载大文件

protected void ResponseFile(string path)//传入服务端文件及路径 大文件下载原理是把文件切成小段数据流下载，微软msdn给出了大文件下载的示例
    {
         iStream = null;//声明文件流
        byte[] buffer = new Byte[10000];//声明缓存区
        int length;//读入缓冲区中的总字节数
        long dataToRead;//剩余要传输到客户端的总字节数
        string filename = (path);//获取文件名及扩展名

        try
        {   //使用指定的路径、创建模式、读/写权限和共享权限
            iStream = new (path, , , );
            dataToRead = iStream.Length;
            Response.ContentType = "application/octet-stream";//指定ContentType
            //Content-Disposition attachment表示以附件方式下载    HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8))解决中文乱码问题
            Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8));
            while (dataToRead > 0)
            {
                if (Response.IsClientConnected)//客户端是否连接
                {
                    length = iStream.Read(buffer, 0, 10000);//读取流到缓存区,
                    Response.OutputStream.Write(buffer, 0, length);//缓存区复制到当前流
                    Response.Flush(); //缓冲区数据先发送到客户端
                    buffer = new Byte[10000];
                    dataToRead = dataToRead - length;
                }
                else
                {
                    dataToRead = -1;
                }
            }
        }
        catch (Exception ex)
        {
            Response.Write("文件下载时出现错误!" + ex.Message);
        }
        finally
        {
            if (iStream != null)
            {
                iStream.Close();
            }
        }
    }