Page redirected too many times ASP.NET - authentication

Question

Dear StackOverflow community,
I am still new with ASP.NET and playing have been playing around and I've encountered an error to authenticate my login where it shows up an error like "Page redirected too many times" and it happen something that are keep looping and I can't figure it out after 2 days.
I've implemented my login using header.acsx so it can be a global authentication to all page.
Here is the code of head.vb:
If String.IsNullOrEmpty(Session(GetSessionKey("UserName"))) Then
Dim userName As String = HttpContext.Current.User.Identity.Name.Split("\")(1)
SessionInitialiser(userName)
End If
Response.Redirect("~/EventRegistration.aspx")
Page_Load function:
Dim adserv As New ActiveDirectory()
Dim userDetails As WebServiceUserPrincipal = adserv.Getuser(userName)
Dim userGroups As String() = adserv.GetUserGroups(userName)
Dim _dt As New DataTable
_dt.Columns.Add("Group")
For Each item As String In userGroups
Dim _row As DataRow = _dt.NewRow()
_row("Group") = item
_dt.Rows.Add(_row)
Next
Session(GetSessionKey("FullName")) = userDetails.DisplayName
Session(GetSessionKey("Groups")) = _dt
Session(GetSessionKey("UserName")) = userName
Session(GetSessionKey("Switch")) = "OK"
Dim filter_auditGroup As String = ConfigurationSettings.AppSettings("FILTER_GROUP")
Dim _adt As New DataTable
_adt.Columns.Add("Group")
For Each item As String In userGroups
If (item = filter_auditGroup) Then
Dim _row As DataRow = _adt.NewRow()
_row("Group") = item
_adt.Rows.Add(_row)
End If
Next
'If _adt.Rows.Count > 0 Then
' Session(GetSessionKey("AuditGroups")) = _adt
'End If
End Sub
Check Access Function
If Not IsPostBack Then
Dim arr As Array = Request.Url.AbsolutePath.Split("/")
Dim page As String = arr(arr.Length - 1).ToString().Split(".")(0) '-- Ballot.aspx, remove .aspx and get Ballot only
Dim signOut As New List(Of String)
signOut.Add("SwitchUser")
signOut.Add("SignOut")
If (Not signOut.Contains(page, StringComparer.OrdinalIgnoreCase)) Then
If (String.IsNullOrEmpty(Session(GetSessionKey("UserName")))) Then
Response.Redirect("~/Default.aspx")
Else
Dim group As DataTable = Session(GetSessionKey("Groups"))
'Dim auditGroup As DataTable = Session(GetSessionKey("AuditGroups"))
Dim adminPage As New List(Of String)
adminPage.Add("BallotProcess")
adminPage.Add("CodeTablePage")
adminPage.Add("MaintainBallotItem")
adminPage.Add("MaintainCodeItem")
adminPage.Add("MaintainItemDetail")
If (adminPage.Contains(page, StringComparer.OrdinalIgnoreCase) And Not CheckAdmin(group)) Then
Response.Redirect("~/EventRegistration.aspx")
End If
'If (page.Equals("AuditPage", StringComparison.OrdinalIgnoreCase) And Not CheckAudit(group)) Then
' Response.Redirect("~/default.aspx")
'End If
End If
End If
End If
Check Admin Function
Private Function CheckAdmin(ByVal group As DataTable) As Boolean
Dim i As Integer
If Not IsNothing(group) Then
For i = 0 To group.Rows.Count - 1
If group.Rows(i)(0) = ConfigurationSettings.AppSettings("FILTER_GROUP") Then
CheckAdmin = True
Session(GetSessionKey("EventAdmin")) = 1
Exit Function
End If
Next
End If
End Function

Answer 1

I have found my answer through countless of debug and all I need to fix this code is just move the Response.Redirect("~/EventRegistration.aspx") into the If Else statement above. This is because when the if else statement execute to get the identity, after its if else statement the value will be Nothing, then it redirect to the page while the page will try to get the identity and it execute again the if else countless of times..
If String.IsNullOrEmpty(Session(GetSessionKey("UserName"))) Then
Dim userName As String = HttpContext.Current.User.Identity.Name.Split("\")(1)
SessionInitialiser(userName)
Response.Redirect("~/EventRegistration.aspx")
End If