Macro - Code Not Detecting All Subfolders

I'm using this piece of code to go through Folders and their Subfolders. It works quite well in going through the first folder and its sub's but does not seem to generate a full list.

I am looking for specific files in these folders, and depending in what folder I place the file, it may or may not detect it. I require the code to go at least 3 levels deep (sometimes more).

FolderName = "C: est folder"
ProcessFiles FolderName, "*.xls"

Code:
'~~> This function was taken from
'~~> http://www.vbaexpress.com/kb/getarticle.php?kb_id=245
Sub ProcessFiles(strFolder As String, strFilePattern As String)
Dim strFileName As String, strFolders() As String
Dim i As Long, iFolderCount As Long

[Code] ......