Response.WriteFile outputs the webpage source instead of the text file

"Response.WriteFile outputs the webpage source instead of the text file"

I have a routine that I figured would work correctly, but it is showing a bizzare behavior.
It basically sends a text file (or other type) to the user's browser to initiate a Save As dialog, but instead of the browser displaying either the SaveAs dialog or the text file, it displays the source code of the webpage.
I can't figure this one out as the path is 100% correct (in fact you can copy the path to a browsers URI box and it displays fine).

I'm stumped on this one.  The path is "E:/SITES/SWG/Web/em/Campaign10011.txt" and the file is fine - no security issues as far as I can tell.  
The webroot is "Web" (but the files will ultimately be coming from a non-web root area of the hard drive for security), though I am not using MapPath as I already know the absolute path.

Private Sub DownloadFile(ByVal filepath As String, ByVal forceDownload As Boolean)
            Dim name As String = Path.GetFileName(filepath)
            Dim ext As String = Path.GetExtension(filepath)
            Dim type As String = ""
            ' set known types based on file extension 
            If ext IsNot Nothing Then
                Select Case ext.ToLower()
                    Case ".htm", ".html"
                        type = "text/HTML"
                    Case ".txt"
                        type = "text/plain"
                    Case ".doc", ".rtf"
                        type = "Application/msword"
                End Select
            End If
 
'TEST area to confirm path is correct
'Me.txtPreview.Text = filepath + vbCrLf + "name: " + name + vbCrLf + "ext: " + ext + vbCrLf + "type: " + type + vbCrLf
 
            If forceDownload Then
                Response.AppendHeader("content-disposition", "attachment; filename=" + name)
            End If
            If type <> "" Then
                Response.ContentType = type
            End If
            Response.WriteFile(filepath)
            Response.End()
        End Sub

Select allOpen in new window