Why would e-mails be sending fine without any problems then all of the sudden I get an error stating "unable to authenticate to smtp server"

I have tried setting up the SMTP auth in the Administrator > General Setup area and it still does not work. But when I take it off and update the settings, e-mails send for a while, then it errors again ... it does not make sense ..

Here is the error:

Hello,

An error was found at 05/19/2006 16:36:02 (1148081762) on line '222' of script
'/var/www/htdocs/issuetracker/include/class.mail_queue.php'.

The error message passed to us was:

'unable to authenticate to smtp server'

A more detailed error message follows:

''

That happened on page 'process_mail_queue.php' from IP Address '' coming from
the page (referrer) ''.

The user agent given was ''.

Sincerely yours, Automated Error_Handler Class

A backtrace is available:

Array ( [0] => Array ( [file] => /var/www/htdocs/issuetracker/include/class.mail_queue.php [line] => 165 [function] => _sendemail [class] => mail_queue [type] => :: [args] => Array (

Regards,