Failed to load viewstate on dynamic user controls?

Hi,
Basically, i can add a photomedia control and youtube control by clicking on respective add buttons. My dynamic user controls can be added successfully EXCEPT for this combination.

youtube - > youtube -> photomedia -> then error when a new user control added!!!
youtube -> photomedia -> youtube -> i can add any other user control. No issue here

If you look at the code below, these 3 controls are added when the first time the page init. Again, if the arrangment is changed other than the arragement above, then i'm able to add a new user control with no issue.

Any help is greatly appreciated.

PS: Been tight down by this issue for the last few weeks...still struggling to resolve it but to no avail :(

Error Message
=============
Failed to load viewstate.  The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request.  For example, when adding controls dynamically, the controls added during a post-back must match the type and position of the controls added during the initial request.

Imports System.Data
Imports System.IO                           'Contains File.Delete() method and FileInfo type for delete purpose.
 
'Google Gdata API namespaces
Imports Google.GData.Client
Imports Google.GData.Extensions
Imports Google.GData.YouTube
 
Partial Class MyAccount_Debug
    Inherits System.Web.UI.Page
 
    'List to keep track of dynamically added user controls.
    Protected Property ctrls() As List(Of String)
        Get
            If Session("ctrls") Is Nothing Then
                Session("ctrls") = New List(Of String)
            End If
            Return CType(Session("ctrls"), List(Of String))
        End Get
        Set(ByVal value As List(Of String))
            Session("ctrls") = value
        End Set
    End Property
 
    'Add new Youtube Modules
    Protected Sub btnAddYoutube_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAddYoutube.Click
 
        Dim Youtube As Youtube = LoadControl("~/UserControl/Youtube.ascx")
        Youtube.ID = "Youtube" & Session("ctrl_id_increment")
 
        'Concat both identifier and ID, will be splitted during page load.
        ctrls.Add(String.Format("{0}|{1}", "Youtube", Session("ctrl_id_increment")))
 
        'Lastly, increment for next control ID
        Session("ctrl_id_increment") += 1
 
        PlaceHolder1.Controls.Add(Youtube)
        PlaceHolder1.Controls.Add(New LiteralControl("<br />"))
 
    End Sub
 
    'Add new Photo Media
    Protected Sub btnAddPhotoMedia_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAddPhotoMedia.Click
 
        Dim PhotoMedia As PhotoMedia = LoadControl("~/UserControl/PhotoMedia.ascx")
        PhotoMedia.ID = "PhotoMedia" & Session("ctrl_id_increment")
 
        'Finally add the controls to the string list.
        ctrls.Add(String.Format("{0}|{1}", "PhotoMedia", Session("ctrl_id_increment")))
 
        'Finally, increment for next control ID
        Session("ctrl_id_increment") += 1
 
        PlaceHolder1.Controls.Add(PhotoMedia)
        PlaceHolder1.Controls.Add(New LiteralControl("<br />"))
 
    End Sub
 
    'Init routine. This will kick off prior to the page_load
    Protected Overrides Sub OnInit(ByVal e As System.EventArgs)
        If Not Page.IsPostBack Then
 
            'Initiate the list class
            ctrls = New List(Of String)
 
            '#######YOUTUBE 1###############
            Dim Youtube As Youtube = LoadControl("~/UserControl/Youtube.ascx")
            Youtube.ID = "Youtube1" 'txtType.Text & txtControlID.Text
            ctrls.Add(String.Format("{0}|{1}", "Youtube", "1"))
 
            '#######YOUTUBE 2###############
            Dim Youtube2 As Youtube = LoadControl("~/UserControl/Youtube.ascx")
            Youtube2.ID = "Youtube3" 'txtType.Text & txtControlID.Text
            ctrls.Add(String.Format("{0}|{1}", "Youtube", "2"))
 
            '##########PHOTO MEDIA###############
            '2) Initialize the user control and assign control ID
            Dim PhotoMedia As PhotoMedia = LoadControl("~/UserControl/PhotoMedia.ascx")
            PhotoMedia.ID = "PhotoMedia2" ' txtType.Text & txtControlID.Text
            ctrls.Add(String.Format("{0}|{1}", "PhotoMedia", "3"))
 
            'Now add the users controls to the placeholder.
            'Problem seen, when arragement in youtube-youtube-photomedia!
            PlaceHolder1.Controls.Add(Youtube)
            PlaceHolder1.Controls.Add(New LiteralControl("<br />"))
            PlaceHolder1.Controls.Add(Youtube2)
            PlaceHolder1.Controls.Add(New LiteralControl("<br />"))
            PlaceHolder1.Controls.Add(PhotoMedia)
            PlaceHolder1.Controls.Add(New LiteralControl("<br />"))
 
            'Next added control will take ID of 4
            Session("ctrl_id_increment") = 4
 
        Else
 
            'Renumerate the list, and add in all the objects (usercontrol, lateral control) to the page's placeholder.
            For Each ctrl As String In ctrls
                Dim c As String() = ctrl.Split("|")
                Select Case c(0)
                    Case "Youtube"
                        Dim Youtube As Youtube = LoadControl("~/UserControl/Youtube.ascx")
                        Youtube.ID = String.Concat(c(0).ToString, c(1).ToString)
                        PlaceHolder1.Controls.Add(Youtube)
 
                    Case "PhotoMedia"
                        Dim PhotoMedia As PhotoMedia = LoadControl("~/UserControl/PhotoMedia.ascx")
                        PhotoMedia.ID = String.Concat(c(0).ToString, c(1).ToString)
                        PlaceHolder1.Controls.Add(PhotoMedia)
 
                End Select
            Next
 
        End If
 
        MyBase.OnInit(e)
 
    End Sub
 
End Class

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