The Autodiscover service couldn't be located.

Please help me out sruggling in this for a long time..

error:  The Autodiscover service couldn't be located.
 my code is
try
            {
                // Connect to Exchange Web Services as user1 at contoso.com.
                ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2010);
                ServicePointManager.ServerCertificateValidationCallback = CertificateValidationCallBack;
                service.Credentials = new WebCredentials("ews@MydomainName.com", "password");
                //service.UseDefaultCredentials = true;
                service.AutodiscoverUrl("ews2@MydomainName.com", ValidateRedirectionUrlCallback);
                //service.Url = new Uri("https://serverName.DomainName.com/ews/Exchange.asmx"); 
               
                // Create the e-mail message, set its properties, and send it touser2@contoso.com, saving a copy to the Sent Items folder.
                EmailMessage message = new EmailMessage(service);
                message.Subject = "Interesting";
                message.Body = "The proposition has been considered.";
                message.ToRecipients.Add("ews1@MydomainName.com");
                message.SendAndSaveCopy();

                // Write confirmation message to console window.
                //Console.WriteLine("Message sent!");
                //Console.ReadLine();
            }
            catch (Exception ex)
            {
                //Console.WriteLine("Error: " + ex.Message);
                //Console.ReadLine();
            }

i browsed-  https://MyserverName.DomainName.com/autodiscover/autodiscover.xml
 it displays

  <?xml version="1.0" encoding="utf-8" ?>
- <Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006">
- <Response>
- <Error Time="17:35:23.3125000" Id="3155127929">
  <ErrorCode>600</ErrorCode>
  <Message>Invalid Request</Message>
  <DebugData />
  </Error>
  </Response>
  </Autodiscover>

please give me a right solution for this as soon as faster