Email error "Unable to read data from the transport connection: net_io_connectionclos

I used code below to send emails everyday from my pc automatically:
Dim myMail As New SmtpClient("email.hcpipa.com") myMail.Credentials = New System.Net.NetworkCredential("mymail", "mypassword") myMail.Send(mail)
IT guy create a account "mymail" in exchange server.
It works for a long time but today has an error said that
System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed.
Is something wrong in server?