System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated.

I have written the above code and im getting an error as below- System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at smtptest._Default.btnSend_Click(Object sender, EventArgs e) in c:\users\administrator\documents\visual studio 2010\Projects\smtptest\smtptest\Default.aspx.cs:line 71 Its working on local but when im hosting my application im getting above error

using (MailMessage mm = new MailMessage("myid@gmail.com","reciverid@yahoo.com"))
                        {
                            mm.Subject = "test";
                            mm.Body = "email testing";
                            
                            mm.IsBodyHtml = false;
                            SmtpClient smtp = new SmtpClient();
                            smtp.Host = "smtp.gmail.com";
                            smtp.EnableSsl = true;
                            NetworkCredential NetworkCred = new NetworkCredential("myid@gmail.com", "pass");
                            smtp.UseDefaultCredentials = true;
                            smtp.Credentials = NetworkCred;
                            smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
                            smtp.Port = 587;
                            smtp.Send(mm);
                            ClientScript.RegisterStartupScript(GetType(), "alert", "alert('Email sent.');", true);
                        }