期末作业出现了解决不了的问题，希望好心人帮帮忙

出问题的代码如下：
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;public partial class Manager_AddCategory : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{ }
protected void Button1_Click(object sender, EventArgs e)
{
BBSManager mybbs = new BBSManager();
bool result = mybbs.AddBBSCategory(TextBox1.Text, TextBox2.Text);
if (result)
Literal1.Text = "论坛类别添加成功！ 请刷新";
}
}
报错是：
错误 1 找不到类型或命名空间名称“BBSManager”(是否缺少 using 指令或程序集引用?) H:\BBS\BBS\Manager\AddCategory.aspx.cs 24 9 H:\BBS\