TeeView Erros

Hi,

I am trying to use a tree view control, I use a button from a form to open a newform which the treeview is on, I can do this once, and select a file, but when I try to reopen the form with the treeview on a second time I get this message:

'Object Reference not set ta an instance of an object'

This is the code I am using:

VB Code:

#Region " Form Load "
 
    Private Sub frmBrowser_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
        lbl_SelectedFile.Text = "Selected File:"
 
        LoadTreeView()
 
    End Sub
#End Region
 
    Private Const DUMMY As String = "DUMMY"
 
    Private Enum ItemType
        Directory = 1
        File = 2
    End Enum
 
    Private Sub tvw_Files_Root_AfterSelect(ByVal sender As System.Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles tvw_Files_Root.AfterSelect
        Try
            With e.Node
                Select Case .Tag
                    Case ItemType.File
                        Dim fi As New FileInfo(.FullPath)
                        DisplayFSIProperties(fi)
                    Case Else
                End Select
            End With
        Catch exp As Exception
            MsgBox(exp.Message, , "after")
            MsgBox(exp.TargetSite, , "after")
        End Try
    End Sub
 
    Private Sub tvw_Files_Root_BeforeExpand(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewCancelEventArgs) Handles tvw_Files_Root.BeforeExpand
        Try
            e.Node.Nodes.Clear()
            AddFolders(e.Node)
            AddFiles(e.Node)
        Catch exp As IOException
            MsgBox(exp.Message, , "before IO")
        Catch exp As Exception
            MsgBox(exp.Message, , "before exp")
        End Try
    End Sub
 
    Private Sub AddFiles(ByVal nod As TreeNode)
        Dim strPath As String = nod.FullPath
        Dim strFile As String
        With nod
            For Each strFile In Directory.GetFiles(strPath)
                With nod.Nodes.Add(Path.GetFileName(strFile))
                    .Tag = ItemType.File
                End With
            Next
        End With
    End Sub
 
    Private Sub AddFolders(ByVal nod As TreeNode)
        Dim strPath As String = nod.FullPath
        Dim strDir As String
        With nod
            For Each strDir In Directory.GetDirectories(strPath)
                With nod.Nodes.Add(Path.GetFileName(strDir))
                    .Tag = ItemType.Directory
                    .Nodes.Add(DUMMY)
                End With
            Next
        End With
    End Sub
 
    Private Sub LoadTreeView()
        Dim strDrive As String
        tvw_Files_Root.Nodes.Clear()
        For Each strDrive In Directory.GetLogicalDrives()
            With tvw_Files_Root.Nodes.Add(strDrive)
                .Nodes.Add(DUMMY)
            End With
        Next
    End Sub
 
    Private Sub DisplayFSIProperties(ByVal fsi As FileSystemInfo)
        Me.lbl_SelectedFile.Text = "Selected File: " & fsi.Name
        FilePath = fsi.FullName
        FileName = fsi.Name
    End Sub
 
    Private Sub cmd_cancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmd_cancel.Click
        Me.Hide()
    End Sub
 
    Private Sub Cmd_ok_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Cmd_ok.Click
        If FilePath = "" Or FileName = "" Then
            MsgBox("A file was not selected" & vbCrLf & "Please Select a file", MsgBoxStyle.OKOnly, "No File Selected")
        Else
            If Male = True Then
                MSPRDir = FilePath
                MainForm.txt_MaleSPRFile.Text = FileName
                MSPRName = FileName
            Else
                If Female = True Then
                    FSPRDir = FilePath
                    MainForm.txt_FemaleSPRFile.Text = FileName
                    FSPRName = FileName
                Else
                    If Male = False And Male = False Then
                        GENDir = FilePath
                        MainForm.txt_Genfile.Text = FileName
                        GENName = FileName
                    End If
                End If
            End If
            Me.Hide()
        End If
 
    End Sub

Any help?

Thanx