Download file using Webclient shows Wrong Data

hi Guyes,
i used following code to download file from secured site but file created on folder @"C:\Downloads\Filename" show HTML tags like This

Servlet Response Message

You are not logged on. Please logon first.

then Actual File content.

     try
            {
                WebClient client = new WebClient();
                client.Credentials = new System.Net.NetworkCredential("username", "password");
                byte[] pageData = client.DownloadData("url");
                string pageHtml = Encoding.ASCII.GetString(pageData);
                Console.WriteLine(pageHtml);

                client.DownloadFile("url", @"C:\Downloads\071213.ACCT");
            }
            catch (WebException webEx)
            {
                Console.WriteLine(webEx.ToString());
                if (webEx.Status == WebExceptionStatus.ConnectFailure)
                {
                    Console.WriteLine("Are you behind a firewall? If so, go through the proxy server.");
                }
            }