help!!!VS报错“当前上下文中不存在名称"GridView2"”莫名其妙啊，明明有这个控件啊。

cs码是:public partial class tongzhi : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string sql = "select * from tongzhi order by tz_time desc";
        SqlDataAdapter myAdap = new SqlDataAdapter(sql, DBHelper.connection);
        DataSet myds = new DataSet();
        myAdap.Fill(myds, "通知报告表");
        GridView2.DataSource = new DataView(myds.Tables[0]);
        GridView2.DataBind();
    }
}


网页源码是:<asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False"
                    Width="960px" AllowPaging="True">
                    <RowStyle HorizontalAlign="Center" VerticalAlign="Middle" />
                    <Columns>
                        <asp:HyperLinkField DataNavigateUrlFields="tz_id"
                            DataNavigateUrlFormatString="tz_content.aspx?id={0}" DataTextField="tz_title"
                            HeaderText="标题" />
                        <asp:BoundField DataField="tz_time" HeaderText="发布时间" />
                        <asp:BoundField DataField="tz_source" HeaderText="来源" />
                        <asp:BoundField DataField="tz_counter" HeaderText="浏览次数" />
                    </Columns>
                    <EditRowStyle HorizontalAlign="Center" VerticalAlign="Middle" />
                </asp:GridView>