为何刷新后页面无法判断session对象？怎么实现发表留言后自动刷新还能判断session

    protected void Page_Load(object sender, EventArgs e)    {        if (!IsPostBack || Convert.ToBoolean(Session["judge"]) == false)        {            bind();            lblName2.Text = "您尚未登录";        }        else        {            Session["judge"] = true;            Session["mail"] = txtUserMail.Text;            Panel1.Visible = false;            Panel2.Visible = true;            lblName.Text = "Hello~" + Convert.ToString(Session["mail"]);            lblName2.Text = Convert.ToString(Session["mail"]) + "您可以发表留言";         }    }

    protected void Button1_Click(object sender, EventArgs e)    {        string dataPath = Server.MapPath("access/DataBase.mdb");        OleDbConnection con = DB.con(dataPath);        con.Open();        OleDbCommand cmd = new OleDbCommand();        cmd.Parameters.Add("@userMail", OleDbType.VarChar, 50);        cmd.Parameters["@userMail"].Value = txtUserMail.Text;        cmd.Parameters.Add("@userPWD", OleDbType.VarChar, 20);        cmd.Parameters["@userPWD"].Value = FormsAuthentication.HashPasswordForStoringInConfigFile(txtuserPWD.Text, "md5");        cmd.CommandText = "select count(*) from userinfo where userMail = @userMail and userPWD = @userPWD";        cmd.Connection = con;        int count = Convert.ToInt32(cmd.ExecuteScalar());        if (count == 1)        {            Session["judge"] = true;            Session["mail"] = txtUserMail.Text;            Panel1.Visible = false;            Panel2.Visible = true;            lblName.Text = "Hello~"+Convert.ToString(Session["mail"]);            lblName2.Text = Convert.ToString(Session["mail"])+"您可以发表留言";            OleDbCommand IDcmd = new OleDbCommand("select ID from userinfo where userMail ='"+txtUserMail.Text+"'", con);            Session["ID"]=Convert.ToString(IDcmd.ExecuteScalar());        }        else        {            Session["judge"] = false;            Response.Write("登录失败!帐号或者密码错误!");        }        con.Close();    }

<asp:Panel ID="Panel1" runat="server" Height="12px" Width="90%">                用户名:<asp:TextBox ID="txtUserMail" runat="server"></asp:TextBox>                密码:<asp:TextBox ID="txtuserPWD" runat="server" TextMode="Password"></asp:TextBox>&nbsp;<asp:Button ID="Button1"                    runat="server" Text="登录" OnClick="Button1_Click" />&nbsp;<asp:Button ID="btnClear" runat="server" OnClick="btnClear_Click"                        Text="清空" />                <asp:LinkButton ID="LinkButton1" runat="server" OnClick="lbtnReg_Click">注册</asp:LinkButton></asp:Panel>            <asp:Panel ID="Panel2" runat="server" Height="12px" Width="90%" Visible="False">                <div style="text-align:left;background:darkorange"><asp:Label ID="lblName" runat="server"></asp:Label><strong>简单留言板(测试版)</strong></div></asp:Panel>            &nbsp;&nbsp;</div>