OK, just took recent code and modified it a bit:
[code]
<%@ Register Assembly="NineRays.WebControls.FlyTreeView" Namespace="NineRays.WebControls"
    TagPrefix="NineRays" %>
    
    
    
    
        
            
            
                
                
                
            
        
    
    
    
        function nodeSelected(sender, oldNode, newNode) {
            alert(newNode.getText());
        }
    
[/code]
Code-behind:
[code]Imports System.IO
Imports NineRays.WebControls
Partial Public Class test1
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        AddNodes(flyTreeView.Nodes, "c:\")
    End Sub
    Public Shared Sub AddNodes(ByVal nodes As FlyTreeNodeCollection, ByVal directoryPath As String)
        Dim directory As New DirectoryInfo(directoryPath)
        If Not directory.Exists Then
            Return
        End If
        Dim subDirectories As DirectoryInfo() = directory.GetDirectories()
        For Each subDir As DirectoryInfo In subDirectories
            Dim ftn As New FlyTreeNode()
            ftn.Text = HttpUtility.HtmlEncode(subDir.Name)
            ftn.Value = subDir.FullName
            nodes.Add(ftn)
            Try
                ' do not set populate on demand for nodes that have no nested directories
                ftn.PopulateNodesOnDemand = subDir.GetDirectories().Length > 0
            Catch ex As Exception
                ' add a child node that shows that there was an exception trying to get its child nodes
                'AddExceptionNode(ftn.ChildNodes, ex)
            End Try
        Next
    End Sub
    Protected Sub flyTreeView_NodeSelected(ByVal sender As Object, ByVal e As NineRays.WebControls.FlyTreeNodeEventArgs) Handles flyTreeView.NodeSelected
        '        ScriptManager.RegisterStartupScript(Me, Me.GetType(), "downloadassssslert", "alert('permission is denied.');", True)
        lbl1.Text = "Updated..."
        UpdatePanel1.Update()
    End Sub
    Protected Sub flyTreeView_PopulateNodes(ByVal sender As Object, ByVal e As NineRays.WebControls.FlyTreeNodeEventArgs) Handles flyTreeView.PopulateNodes
        AddNodes(e.Node.ChildNodes, e.Node.Value)
    End Sub
End Class[/code]