Object Refenece

I been asking for help and my post gets put at the end of the line I guess. Any way I have tring to find out what part of my VB.NET that I have has an object = nothing. I keep getting an "Object reference not set to a instance of a object. Could some one please look at this and maybe I can get this fixed.
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Imports System.IO

Partial Class MapNet_Upload

    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        If User.Identity.IsAuthenticated = False Then
            Server.Transfer("Error.aspx?error=1")
        End If

        If Roles.IsUserInRole("MapNet") = False Then
  ...