Private Sub Getfiles(ByVal Folder As IO.DirectoryInfo, 
                     ByVal Searchpattern As String,
                     ByVal files As List(Of String), errors As List(Of String))
 
        Dim SubFldInf As IO.DirectoryInfo
        Dim FileInf As IO.FileInfo
 
        'alle Dateien des übergebenen Ordners auflisten
        Try
            For Each FileInf In Folder.EnumerateFiles(Searchpattern)
                Try
                    files.Add(FileInf.FullName)
                Catch ex As Exception
                    errors.Add(FileInf.FullName)
                End Try
            Next FileInf
 
            'Alle untergeordneten Ordner bearbeiten
            For Each SubFldInf In Folder.EnumerateDirectories()
                Try
                    Getfiles(SubFldInf, Searchpattern, files, errors)
                Catch ex As Exception
                    errors.Add(SubFldInf.FullName)
                End Try
            Next SubFldInf
        Catch ex As Exception
            errors.Add(Folder.FullName)
        End Try
End Sub

Dim files As New List(Of String), errors As New List(Of String)
Dim fld As String = "C:\users"
 
Getfiles(New IO.DirectoryInfo(fld), "*.txt", files, errors)