Browse for folder error

Good morning, afternoon or evening (depending on wherer you are),

How do I get the function below to get the folder name below to pass to the sub?

Option Explicit

Sub GetFolderName()

Dim FolderName              As String
Dim sFName                  As String
Dim sFPath                  As String

FolderName = BrowseForFolder

sFName = Dir$(FolderName \ "*.txt")

Do While sFName <> ""

MsgBox (sFName)

'Get next file name
    sFName = Dir$
    sFPath = FolderName
    sFNamePath = sFPath + sFName

Loop

End Sub

Function BrowseForFolder(Optional OpenAt As Variant) As Variant
     'Function purpose:  To Browser for a user selected folder.
     'If the "OpenAt" path is provided, open the browser at that directory
     'NOTE:  If invalid, it will open at the Desktop level
     
    Dim ShellApp As Object
     
     'Create a file browser window at the default folder
    Set ShellApp = CreateObject("Shell.Application"). _
    BrowseForFolder(0, "Please choose a folder", 0, OpenAt)
     
     'Set the folder to that selected.  (On error in case cancelled)
    On Error Resume Next
    BrowseForFolder = ShellApp.self.Path
    On Error GoTo 0
     
     'Destroy the Shell Application
    Set ShellApp = Nothing
     
     'Check for invalid or non-entries and send to the Invalid error
     'handler if found
     'Valid selections can begin L: (where L is a letter) or
     '\\ (as in \\servername\sharename.  All others are invalid
    Select Case Mid(BrowseForFolder, 2, 1)
    Case Is = ":"
        If Left(BrowseForFolder, 1) = ":" Then GoTo Invalid
    Case Is = "\"
        If Not Left(BrowseForFolder, 1) = "\" Then GoTo Invalid
    Case Else
        GoTo Invalid
    End Select
     
    Exit Function
     
Invalid:
     'If it was determined that the selection was invalid, set to False
    BrowseForFolder = False
     
End Function

Right now it gives me nothing. I keep getting Run-time error '13': Type mismatch. When I remove the loop and put FolderName in the MsgBox it gives me the correct folder that I chose, so the function works, but I can't get it to work with the loop. Can anyone help me out?

Thanks.

abousetta