' scrollbar 
    Private Sub Panel1_Scroll(sender As Object, e As ScrollEventArgs) Handles Panel1.Scroll
        Panel1.BackColor = System.Drawing.Color.Empty
        Panel1.BackColor = System.Drawing.Color.Transparent
    End Sub
 
    Private Sub Panel1_MouseScroll(sender As Object, e As MouseEventArgs) Handles Panel1.MouseWheel
        Panel1.BackColor = System.Drawing.Color.Empty
        Panel1.BackColor = System.Drawing.Color.Transparent
    End Sub

            If System.IO.File.Exists(Temp_file) = True Then System.IO.File.Delete(Temp_file)
            System.IO.File.Create(Temp_file)

The process cannot access the file 'C:\Users\Administrador\AppData\Local\Temp\PlayList_temp.txt' because it is being used by another process.

  Public Sub C1Button2_Click(sender As Object, e As EventArgs) Handles Button1.Click
 
        If Not playerargs = Nothing Then
 
            Dim Str As String
            Dim Pattern As String = ControlChars.Quote
            Dim ArgsArray() As String
            Dim Temp_file As String = System.IO.Path.GetTempPath & "\PlayList_temp.txt"
            Dim objWriter As New System.IO.StreamWriter(Temp_file)
 
            Str = Replace(playerargs, " " & ControlChars.Quote, "")
            ArgsArray = Split(Str, Pattern)
 
            If System.IO.File.Exists(Temp_file) = True Then System.IO.File.Delete(Temp_file)
            System.IO.File.Create(Temp_file)
 
        For Each folder In ArgsArray
            If Not folder = Nothing Then
                Dim di As New IO.DirectoryInfo(folder)
                Dim files As IO.FileInfo() = di.GetFiles("*")
                    Dim file As IO.FileInfo
 
                For Each file In files
                    ' command to writleline
                    'Console.WriteLine("File Name: {0}", file.Name)
                    'Console.WriteLine("File Full Name: {0}", file.FullName)
                    objWriter.Write(file.FullName)
                    objWriter.Close()
                Next
            End If
            Next
 
        If randomize.Checked = True Then
                RandomiseFile(Temp_file)
        End If
 
        Process.Start(userSelectedPlayerFilePath, playerargs)
        If autoclose.Checked = True Then
            Me.Close()
        End If
        Else
        MessageBox.Show("You must select at least one folder...", My.Settings.APPName)
        End If
    End Sub

....
If Not playerargs = Nothing Then
    ....
    Dim Temp_file As String = System.IO.Path.GetTempPath & "\PlayList_temp.txt"
 
    Using objWriter As New System.IO.StreamWriter(Temp_file, false)
        For Each folder In ArgsArray
            If Not folder = Nothing Then
                Dim di As New IO.DirectoryInfo(folder)
                Dim files As IO.FileInfo() = di.GetFiles("*")
                Dim file As IO.FileInfo
                For Each file In files
                    ' command to writleline
                    'Console.WriteLine("File Name: {0}", file.Name)
                    'Console.WriteLine("File Full Name: {0}", file.FullName)
                    objWriter.Write(file.FullName)
                    ' objWriter.Close() 
                Next
            End If
        Next
    End Using ' Flush, close and dispose the objWriter
    ....

            Dim Expresión As String = String.Format("{0}[^{0}]+?{0}", Convert.ToChar(32))
 
            'Esta variable simula la que tu creas en tu aplicación'
            Dim Comando As String = String.Format(playerargs, Convert.ToChar(32))
 
            For Each x As Match In Regex.Matches(Comando, Expresión)
                MessageBox.Show(x.Value)
            Next
 

            Str = Replace(playerargs, " " & ControlChars.Quote, "")
            ' El contenido de Cadena queda así:    C:\Ruta 1"C:\Ruta 2"C:\Ruta 3"etc..."

            Dim Str As String
            ' Elimino los espacios entre argumentos
            Str = Replace(playerargs, " " & ControlChars.Quote, ControlChars.Quote)
            ' El contenido de Cadena queda así: "C:\Ruta 1""C:\Ruta 2""Más rutas..."
 
            ' El patrón delimitador (comilla)
            Dim Pattern As String = ControlChars.Quote
 
            Dim ArgsArray() As String 'Creamos un array 
 
            ArgsArray = Split(Str, Pattern) 'Llenamos el array con las cadenas cortadas.
 
            ' Mostramos como ha quedado el resultado
            For Each folder In ArgsArray
                If Not folder = Nothing Then
                    Console.WriteLine(folder)
                    MessageBox.Show(folder)
                End If
 
 
            If randomize.Checked = True Then
                '  RandomiseFile("c:\1.txt")
            End If