Sending Mail Failure using {System.Net.Mail.SmtpException: Authentication failed.}

HI guys
I am using

System.Net.Mail;

to send mails in windows application .
all my credentials are right but i am getting "Authentication failed" Error message..

I have tried a lot but it didn't worked .. Can anyone Help me pls
 
this is the error message i am getting in depth...

{System.Net.Mail.SmtpException: Authentication failed.
at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)
at System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint)
at System.Net.Mail.SmtpClient.GetConnection()
at System.Net.Mail.SmtpClient.Send(MailMessage message)

here is the code:

SmtpClient client = new SmtpClient();
                MailMessage msg = new MailMessage();
               
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.EnableSsl = false;
                client.Host =  "mail.xx.com";
                client.Port =  25;
 
                System.Net.NetworkCredential credentials = new System.Net.NetworkCredential("username@xx.com", "pwd");
                client.UseDefaultCredentials = false;
                client.Credentials = credentials;
                msg.From = new MailAddress("ams@xx.com",System.Text.Encoding.UTF8);
                msg.To.Add(xx@gmail.com);
                msg.Subject = Subject;
                msg.SubjectEncoding = System.Text.Encoding.UTF8;
                msg.Priority = MailPriority.High;
                msg.Body = Body;
                msg.BodyEncoding = System.Text.Encoding.UTF8;
                msg.IsBodyHtml = true;
 
                msg.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
                client.Send(msg);

Thanks In advance
 
[Edit]Code block added[/Edit]