FTP Connection Closed Error

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I have written a Windows service that periodically lists the contents of an
FTP directory until a new file becomes available. Then, it gets the new file
and writes it to the local server. Most of the time, this works fine, but
occasionally I get the following exception while getting the directory
listing:

Message: The underlying connection was closed: An unexpected error occurred
on a receive.
Source: System, Void SyncRequestCall back(System.Obj ect)
Inner Exception:
Stack Trace:
at System.Net.FtpW ebRequest.SyncR equestCallback( Object obj)
at System.Net.FtpW ebRequest.Reque stCallback(Obje ct obj)
at System.Net.Comm andStream.Abort (Exception e)
at System.Net.FtpW ebRequest.Finis hRequestStage(R equestStage stage)
at System.Net.FtpW ebRequest.GetRe sponse()
at RiverFlowBackup .FileTransfer.L istFiles()
at RiverFlowBackup .FileTransfer.G etNameOfLastest File()
at RiverFlowBackup .FileTransfer.W aitForNewFile()
at RiverFlowBackup .RFBService.tim erExecute_Elaps ed(Object sender,
ElapsedEventArg s e)

I'm beginning to think that when I get this error, the request for the
directory list is taking longer than usual and some timeout period of around
15 seconds is causing the connection to close.

I have the KeepAlive property of the FTP object set to FALSE and the TimeOut
property is set to 3 minutes (180000ms). Below is the relevent code:

private ArrayList ListFiles()
{
ArrayList fileNames = new ArrayList();
// Build the FTP request to get the directory listing
FtpWebRequest request =
BuildRequest(We bRequestMethods .Ftp.ListDirect ory);
// Execute the request and get the response from the FTP server
FtpWebResponse response = null;
Stream responseStream = null;
StreamReader reader = null;

try
{
// Get the response from the FTP server
response = (FtpWebResponse )request.GetRes ponse();

// Access the contents of the response
responseStream = response.GetRes ponseStream();
reader = new StreamReader(re sponseStream);

// Read each line of the response contents. Each line
contains one file name.
while (!reader.EndOfS tream)
{
string fileName = reader.ReadLine ();

// Verify that the file name matches the format defined
in the application
// configuration settings. If it does, add it to the
file name array that
// is returned by this function.
Regex ex = new Regex(ftpFileFi lter);
if (ex.IsMatch(fil eName))
fileNames.Add(f ileName);
}
}
finally
{
// Release resources
if (reader != null)
reader.Close();

if (responseStream != null)
responseStream. Close();

if (response != null)
response.Close( );
}

return fileNames;
}
private FtpWebRequest BuildRequest(st ring method)
{
return this.BuildReque st(method, String.Empty);
}
private FtpWebRequest BuildRequest(st ring method, string fileName)
{
// Build the FTP request object
string filePath = ftpPath + fileName;
FtpWebRequest request =
(FtpWebRequest) FtpWebRequest.C reate(filePath) ;

request.Method = method;
request.Credent ials = new NetworkCredenti al(ftpUserName,
ftpPassword);
request.Timeout = ftpTimeout;
request.CachePo licy = new
System.Net.Cach e.RequestCacheP olicy(System.Ne t.Cache.Request CacheLevel.Bypa ssCache);
request.KeepAli ve = false;
request.UseBina ry = (ftpTransferTyp e == TransferTypeEnu m.Binary);
request.Proxy = null;

return request;
}
Thank you in advance for your help.