VS 2010 [RESOLVED] List(of T).Concat not working

Private Sub btnOpen_Click(sender As System.Object, e As System.EventArgs) Handles btnOpen.Click
        dlgOpen.InitialDirectory = "C:\Users\USUARIO\Desktop\Word Lists\"
        dlgOpen.Title = "Choose which file to work on"
        dlgOpen.Filter = "Text Files(*.txt)|*.txt|CSV Files(*.csv)|*.csv"
        dlgOpen.Multiselect = True
        Dim LineCount As Integer = 0
        Dim CheckCancel As Integer
        CheckCancel = dlgOpen.ShowDialog()
        If CheckCancel <> DialogResult.Cancel Then
            LblFile.Text = Path.GetFileName(dlgOpen.FileName)
            Dim MyFileAndPath As String = dlgOpen.FileName
            'load the file
            TheMasterList = Nothing ' this is declared publicly at the beginning of the class.
            ListBox1.Items.Clear()
            For Each WordList As String In dlgOpen.FileNames
                Dim TheNewList As List(Of String) = (File.ReadAllLines(MyFileAndPath).ToList())
                If TheMasterList Is Nothing Then
                    TheMasterList = TheNewList
                Else
                    [COLOR="#FF0000"][B]TheMasterList.Concat(TheNewList)[/B][/COLOR]
                End If
            Next
            LineCount += TheMasterList.Count
            lblLines.Text = LineCount.ToString
            ListBox1.Items.AddRange(TheMasterList.ToArray)
        End If
    End Sub