Vista - FTP Connection Closed Error

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 SyncRequestCallback(System.Object)
Inner Exception:
Stack Trace:
at System.Net.FtpWebRequest.SyncRequestCallback(Object obj)
at System.Net.FtpWebRequest.RequestCallback(Object obj)
at System.Net.CommandStream.Abort(Exception e)
at System.Net.FtpWebRequest.FinishRequestStage(RequestStage stage)
at System.Net.FtpWebRequest.GetResponse()
at RiverFlowBackup.FileTransfer.ListFiles()
at RiverFlowBackup.FileTransfer.GetNameOfLastestFile()
at RiverFlowBackup.FileTransfer.WaitForNewFile()
at RiverFlowBackup.RFBService.timerExecute_Elapsed(Object sender,
ElapsedEventArgs 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(WebRequestMethods.Ftp.ListDirectory);


// 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.GetResponse();

// Access the contents of the response
responseStream = response.GetResponseStream();
reader = new StreamReader(responseStream);

// Read each line of the response contents. Each line
contains one file name.
while (!reader.EndOfStream)
{
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(ftpFileFilter);
if (ex.IsMatch(fileName))
fileNames.Add(fileName);
}
}
finally
{
// Release resources
if (reader != null)
reader.Close();

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

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

return fileNames;
}


private FtpWebRequest BuildRequest(string method)
{
return this.BuildRequest(method, String.Empty);
}


private FtpWebRequest BuildRequest(string method, string fileName)
{
// Build the FTP request object
string filePath = ftpPath + fileName;
FtpWebRequest request =
(FtpWebRequest)FtpWebRequest.Create(filePath);

request.Method = method;
request.Credentials = new NetworkCredential(ftpUserName,
ftpPassword);
request.Timeout = ftpTimeout;
request.CachePolicy = new
System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.BypassCache);
request.KeepAlive = false;
request.UseBinary = (ftpTransferType == TransferTypeEnum.Binary);
request.Proxy = null;

return request;
}


Thank you in advance for your help.