using session state dont work properly - asp.net

Question

i am still new to using session state, i want to convert page name into and integer according to a database table
a function then compares "X" and "Y" to check if a user have the right to view this page
i know this is not the best way of managing website security, but it is like "training on how to use the session"
what have i done wrong
Partial Class advancedsearch
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Try
Label1.Text = Session("username").ToString
Label3.Text = Session("role").ToString
Label4.Text = System.IO.Path.GetFileName(Request.Url.ToString())
Catch ex As Exception
Response.Redirect("login.aspx")
End Try
If Label1.Text = "" Then
Response.Redirect("login.aspx")
End If
Dim x As Integer = Int32.Parse(Label3.Text)
Dim y As Integer = Int32.Parse(DropDownList1.SelectedItem.ToString)
If x < y Then Response.Redirect("login.aspx")
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
Response.Redirect("default.aspx")
End Sub
End Class

Answer 1

try putting the comparison part in pre render complete
Protected Sub Page_PreRenderComplete(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRenderComplete
Dim x As Integer = Int32.Parse(Label3.Text)
Dim y As Integer = Int32.Parse(DropDownList1.SelectedItem.ToString)
If x < y Then Response.Redirect("login.aspx")
End Sub