Webclient unable to connect to remote server - vb.net

Question

I am trying to read a text file on a website using a PC that appears to be behind a proxy server. Originally I had 407 errors but then I added;
<system.net>
<defaultProxy useDefaultCredentials="true">
<proxy usesystemdefault="True" />
</defaultProxy>
</system.net>
to the app.config and now I get "Unable to connect to the remote server".
My code is:
' Make a WebClient.
myWebClient = New System.Net.WebClient
' Get the indicated URI.
Dim response As Stream = myWebClient.OpenRead("mySite/myfile.txt")
' Read the result.
Dim objreader As New IO.StreamReader(response)
If I enter "mySite/myfile.txt" into a browser from the same PC the website file is displayed on the screen.
Do I have a code error or is there a way my app can get around this?
I have solved the problem by reverting to the VB5 version which uses API calls to download the text file before reading it.
Thanks Randy Birch.
'//API to download file
Private Declare Function URLDownloadToFile Lib "urlmon" Alias "URLDownloadToFileA" _
(ByVal pCaller As Integer, ByVal szURL As String, ByVal szFileName As String, ByVal dwReserved As Integer, ByVal lpfnCB As Integer) As Integer
Private Declare Function DeleteUrlCacheEntry Lib "Wininet.dll" Alias "DeleteUrlCacheEntryA" (ByVal lpszUrlName As String) As Integer
Private Const ERROR_SUCCESS As Integer = 0
Private Const BINDF_GETNEWESTVERSION As Integer = &H10
'//
Private Function DownloadFileAPI(ByRef sSourceUrl As String, ByRef sLocalFile As String) As Boolean
'http://vbnet.mvps.org/index.html?code/internet/urldownloadtofile.htm
'http://vbnet.mvps.org/index.html?code/internet/urldownloadtofilenocache.htm
Call DeleteUrlCacheEntry(sSourceUrl)
'Download the file. BINDF_GETNEWESTVERSION forces
'the API to download from the specified source.
'Passing 0& as dwReserved causes the locally-cached
'copy to be downloaded, if available. If the API
'returns ERROR_SUCCESS (0), DownloadFile returns True.
DownloadFileAPI = URLDownloadToFile(0, sSourceUrl, sLocalFile, BINDF_GETNEWESTVERSION, 0) = ERROR_SUCCESS
End Function
and in the code;
Dim retbol As Boolean
Dim URL As String = "mySite/myFiletodownload"
fsavename = "mysavefile" 'path\filename to save downloaded file to.
Try
'This should return true or false so might not trigger an exception
retbol = DownloadFileAPI(URL, fsavename)
'etc