求助：session问题！！！

我在index页面的protected void Page_Load(object sender, EventArgs e)里初始化 this.Session["UserName"] = "www.silverfin.com";
在Login.ascx.cs里的一部分代码是这样的
public partial class Login : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{

{
string Uname = txtUname.Text;
string Upwd = txtUPwd.Text;
string yanzhengma = txtYanZhenMa.Text;

if (Uname == "" || Uname == null)
lblMessage.Text = "请输入用户名";
else if (Upwd == "" || Upwd == null)
lblMessage.Text = "请输入密码";
else if (yanzhengma == "" || yanzhengma == null)
lblMessage.Text = "请输入验证码";
else if (yanzhengma.ToString().ToLower() != Session["VerifyCode"].ToString().ToLower())
lblMessage.Text = "验证码错误";
else
{

bool b = UserBLL.FindUser(Uname, Upwd);
if (b)
{
User u = UserBLL.getUser(Uname, Upwd);
int UId = u.UId;

int RoleId = UserBLL.selectRoleId(UId);
if (RoleId == 1)
{
lblMessage.Text = "管理员请从后台登录";
}
else if (RoleId == 3)
{
lblMessage.Text = "用户名或密码错误";
}
else
{
Session["UserName"] = Uname;
Session["UserId"] = u.UId;
Response.Redirect("Default.aspx");

在母板 MasterPage2.master.cs里的部分代码是：
protected void Page_Load(object sender, EventArgs e)
{
if (Session["UserName"] == null)
{
Response.Redirect("Index.aspx");
}
else
{
if (Session["UserName"].ToString() == "www.silverfin.com")
{
Label1.Text = "你好，欢迎光临银枫居家饰有限公司！";
LinkButton1.Text = "登录";

}
else
{
Label1.Text = Session["UserName"].ToString() + "你好，欢迎光临银枫居家饰有限公司！";
int uid = Convert.ToInt32(Session["UserId"]);
LinkButton1.Text = "注销";
}

}

当用户登录成功的时候，转换到default页面可是并没有显示 Label1.Text = Session["UserName"].ToString() + "你好，欢迎光临银枫居家饰有限公司！";这个结果！！！。在default和index页面里都加载了MasterPage2.master了的。index有this.Session["UserName"] = "www.silverfin.com"，可在登录的时候给session重新赋值了，Session["UserName"] =Uname（string Uname = txtUname.Text;）;为什么感觉系统默认为Session["UserName"] = "www.silverfin.com，对重新赋值怎么没用啊，我就是参照别的网站这样做的，请大家帮帮我啊，昨天已经搞了一天了。session的值到底有什么讲究方法？