Unfornatually it generates some errors.

1. If subfolders become involved in a folder selected then the next folder selected becomes out of numerical order.

2. If subfolders become involved in a folder selected the Cancel button has to be repeated and repeated depending on how many folders you have added.

Code:

Sub MainList()
'Updateby Extendoffice
Set folder = Application.FileDialog(msoFileDialogFolderPicker)
If folder.Show <> -1 Then Exit Sub
xDir = folder.SelectedItems(1)
Call ListFilesInFolder(xDir, True)
End Sub

Sub ListFilesInFolder(ByVal xFolderName As String, ByVal xIsSubfolders As Boolean)
Dim xFileSystemObject As Object
Dim xFolder As Object
Dim xSubFolder As Object
Dim xFile As Object
Dim rowIndex As Long
Set xFileSystemObject = CreateObject("Scripting.FileSystemObject")
Set xFolder = xFileSystemObject.GetFolder(xFolderName)
rowIndex = Application.ActiveSheet.Range("A65536").End(xlUp).Row + 1
For Each xFile In xFolder.Files
Application.ActiveSheet.Cells(rowIndex, 1).Formula = xFile.Name
rowIndex = rowIndex + 1
Next xFile
If xIsSubfolders Then
For Each xSubFolder In xFolder.SubFolders
ListFilesInFolder xSubFolder.Path, True
Next xSubFolder
End If
Set xFile ...