缺少using指令或者程序集引用

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;
using computerlab;
using System.Data.SqlClient;

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

}
protected void Button1_Click(object sender, EventArgs e)
{
if (Page.IsValid == true)
{

///定义类并获取用户的登陆信息
computerlab.User user = new computerlab.User();
SqlDataReader recu = user.GetUserLogin(UserName.Text.Trim(),
computerlab.User.Encrypt(Password.Text.Trim()));

///判断用户是否合法
if (recu.Read())