gridview在后台无法显示

我是新手，正在学vs2005， 我再用gridview时发现我页面声明的gridview1在该页面的cs中找不到，就无法调用gridview1的功能我是不是少引用了什么还是哪出错了，希望帮我解决一下，谢谢aspx:
<asp:GridView ID="GridView1" runat="server" AllowPaging="True" AllowSorting="True" AutoGenerateDeleteButton="True" AutoGenerateEditButton="True">
            <Columns>
                <asp:BoundField DataField="ST_Student_id" HeaderText="学号" ReadOnly="True" />
                <asp:BoundField DataField="ST_Student_name" HeaderText="姓名" />
                <asp:BoundField DataField="ST_Student_sex" HeaderText="性别" />
                <asp:BoundField DataField="ST_Student_nation" HeaderText="民族" />
                <asp:BoundField DataField="ST_Student_birthday" HeaderText="出生日期" />
                <asp:BoundField DataField="ST_Student_time" HeaderText="入学时间" />
                <asp:BoundField DataField="ST_Student_classid" HeaderText="班级" />
                <asp:BoundField DataField="ST_Student_home" HeaderText="生源" />
                <asp:BoundField DataField="ST_Student_else" HeaderText="备注" />
            </Columns>
        </asp:GridView>
cs的引用
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Configuration;