未能找到类型或命名空间名称“DBUser”(是否缺少 using 指令或程序集引用?)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;

public partial class Login : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void userLogin(object sender, EventArgs e)
    {

        int flag = 0;
        string AUser = " ", Apwd = " ", Arnd = " ";
        AUser = this.txtUser.Text.Trim().Replace(" < ", " ' ' ").Replace("> ", " ' ' ");
        Apwd = this.txtPwd.Text.Trim();
        Arnd = this.txtRnd.Text.Trim();
        if (AUser == " ")
            Response.Write(" <script   language=javascript> alert( '请输入您的管理帐号！ '); </script> ");
        if (Apwd == " ")
            Response.Write(" <script   language=javascript> alert( '请输入您的管理密码！ '); </script> ");
        if (Arnd != (string)Session["CheckCode "])
            Response.Write(" <script   language=javascript> alert( '您输入的验证码错误！ '); </script> ");
        else
        {
            DBUser ALogin = new DBUser();
            flag = ALogin.AdminLogin(AUser, Apwd);
            if (flag == 1)
                Response.Write(" <script   language=javascript> alert( '您输入的密码错误!请重新登陆!! '); </script> ");
            else if (flag == 2)
                Response.Write(" <script   language=javascript> alert( '对不起!登陆用户名为[ " + AUser + "]的用户不存在! '); </script> ");
            else if (flag == 3)
                Response.Write(" <script   language=javascript> alert( '您的输入中有非法字符，请检查输入！ '); </script> ");
            else if (flag == 4)
            {
                Session["AdminUser "] = AUser;
                Response.Redirect("default.aspx ");
            }
        }
    }
//数据访问层：
     public   int   AdminLogin(string   username,string   password)
     {
            int   flaglogin=0;
            string   exMessage= " ";
            SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=Domain name;Integrated Security=True");
            string sql = "select * from News";
            try
            {
            conn.Open();
            SqlCommand mycmd = new SqlCommand(sql, conn);
            mycmd.CommandType=CommandType.StoredProcedure;
            SqlParameter   paraUname=new   SqlParameter( "@username ",SqlDbType.VarChar,50);
            paraUname.Value=username;
            mycmd.Parameters.Add(paraUname);
            SqlDataReader   mysdr=mycmd.ExecuteReader();
            mysdr.Read();
            if   (mysdr.HasRows)
            {
                string   AUser=mysdr[ "AdminUser "].ToString().Trim();
                string   APWD=mysdr[ "AdminPWD "].ToString().Trim();
                password=System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(password, "md5 ");//进行MD5加密以便验证
                if(password!=APWD)
            {
                flaglogin=1;
            }
            else
            flaglogin=4;
            }
                else
                flaglogin=2;
                mysdr.Close();
            }
            catch(Exception   ex)
            {
                exMessage=ex.Message;
                if   (ex.GetBaseException()   is   System.Web.HttpRequestValidationException)
                exMessage= "您的输入中有非法字符！ ";
            }
            finally
            {

                conn.Close();
            }
                if   (exMessage.Length> 0)
                flaglogin=3;
                return   flaglogin;
        }

    } --------------------编程问答-------------------- 缺少引用，添加引用即可 --------------------编程问答-------------------- 缺少引用，添加引用即可

补充：.NET技术 ,  C#