System.Net.Sockets.SocketException error while using WebClient

[zooferic]

I am getting followed error while first time get report on different server afterwards i refresh web page again report appearing properly.What can be cause?

System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 10.6.240.151:80

protected void Page_Load(object sender, EventArgs e)
{
    Response.Clear();
    try
    {
        if (Request.QueryString.Keys.Count == 0)
            Response.End();
        else
        {
            string uri = ConfigurationSettings.AppSettings["uri"] + Request.QueryString;
            WebRequest request = WebRequest.Create(uri);
            WebResponse responses = request.GetResponse();
            byte[] response = new System.Net.WebClient().DownloadData(uri);
            Response.ContentType = "application/pdf";
            Response.AppendHeader("Content-Disposition", responses.Headers.GetValues(2)[0]);
            Response.BinaryWrite(response);
            Response.Flush();
            Response.End(); 
        }
    }
    catch {
        throw exception;
    }
}

<?xml version="1.0"?>
<configuration>
  <appSettings>
    <add key="uri" value="http://test.domain.com/report/?" />
  </appSettings>
  <system.web>
    <compilation debug="true" targetFramework="4.0"/>
    <httpRuntime/>
    <pages controlRenderingCompatibilityVersion="4.0"/>
  </system.web>
  <system.net> 
     <defaultProxy> 
        <proxy proxyaddress = "http://10.6.240.151:80" bypassonlocal = "True" /> 
     </defaultProxy> 
  </system.net>
</configuration>