The SMTP server requires a secure connection or the client was not authenticated. The server response was: mail.thehosting4u.com ESMTP MailEnable Service, Version: 6.9-- denied access

I am trying to sending email but it gives me following error.

The SMTP server requires a secure connection or the client was not authenticated. The server response was: mail.thehosting4u.com ESMTP MailEnable Service, Version: 6.9-- denied access at 09/16/13 12:05:02

please help me. asap

thanks,

Mohit