ADO.NET使用三层架构实现用户登录出现错误，提示未定义Common，怎么解决

Question

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.Common;
using NewsModels;
using System.Data.SqlClient;
using NewsBLL;

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

    }

    protected void btnLogin_Click(object sender, EventArgs e)
    {
        if (Page.IsValid)
        {
            string loginName = txtLoginName.Text.Trim();
            string loginPwd = txtLoginPwd.Text.Trim();
            User user;
            if (UserManager.UserLogin(loginName, loginPwd, out user))
            {
                if (user.Role == "2")
                {
                    System.Web.Security.FormsAuthentication.SetAuthCookie(user.LoginName, false);
                    FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(1, user.LoginName, DateTime.Now, DateTime.Now.AddMinutes(30), false, "admin");
                    string hashticket = FormsAuthentication.Encrypt(ticket);
                    HttpCookie cookie = new HttpCookie(FormsAuthentication.FormsCookieName,hashticket);
                    Response.Cookies.Add(cookie);
                    if (Request["ReturnUrl"] != null)
                    {
                        Response.Redirect(Request["ReturnUrl"]);
                    }
                    else
                    {
                    Response.Redirect("~/Admin/Default.aspx");
                    }

                }
                else
                {
               Common.Message.RegScript(this,"你不是管理员，无权访问！");
                }

            }
            else
            {
             Common.Message.ReScript(this,"用户名或密码不正确，请重新输入！");
            }
        }
    } 
}

}