SelectedNodeChanged Event Not Fired for TreeView

I have a .Net 2.0 treeview control on my ASP.net website.
the issue i have is that when a dynamically created treenode has been created and then is clicked..
the page is not posted back and the SelectedNodeChanged event does not get fired.
below i have shown my code that created the treenode
i have tried setting the TreeNode SelectAction as both select and selectAction neither of which makes any difference is firing the SelectedNodeChanged event.

Code:

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Private Sub DotvNavigation()
        'build the tvNavigation

        tvNavigation.Nodes.Clear()
        Dim RootTreeNode As New TreeNode
        RootTreeNode.Text = "System Name"
        tvNavigation.Nodes.Add(RootTreeNode)

        datareader = GetSqlData.GetNodes4Navigation
        While datareader.Read
            If datareader.HasRows = True Then
                Dim iCount As Integer
                Dim iParentMenuID As Integer = datareader(0)
                Dim sMenuItemName As String = datareader(1)
                Dim iMenuID As Integer = datareader(2)

                Dim TreeNode As New TreeNode
                TreeNode.Text = sMenuItemName
                TreeNode.Value = iMenuID


                'TreeNode.SelectAction = TreeNodeSelectAction.Select
                TreeNode.SelectAction = TreeNodeSelectAction.SelectExpand

                RootTreeNode.ChildNodes.Add(TreeNode)
             
        End While

    End Sub

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any1 any ideas?