Trouble using PEAR"s Mail_Queue

I'm trying to implement PEAR's Mail_Queue package to queue some emails for a web application. I've used the documentation at http://pear.php.net/manual/en/package.mail.mail-queue.mail-queue.tutorial.php to write a small test script.

My problem is that the database is not being updated, and it's not producing errors.

EDIT

// mail_queue db options

$db_options['type'] = 'mdb2';

$db_options['dsn'] = DSN;

$db_options['mail_table'] = 'mail_queue';



// mail_queue sending options

$mail_options['driver'] = 'smtp';

$mail_options['host'] = 'smtp.gmail.com';

$mail_options['port'] = 25;

$mail_options['localhost'] = $host;

$mail_options['auth'] = true;

$mail_options['user'] = MAILUSER;

$mail_options['pass'] = MAILPASS;



require "Queue.php";



$mail_queue =& new Mail_Queue($db_options,$mail_options);



$from = 'someone@domain.ca';

$to = 'martin@starmedia.ca';

$message = 'This is a test';



$headers = array('From' => $from,

    'To' => $to,

    'Subject' => 'Someone has sent you an email!');



$mime =& new Mail_mime();

$mime->setTXTBody($message);

$body = $mime->get();



$headers = $mime->headers($headers,true);

print $mail_queue->put($from,$to,$headers,$body);

This produces the error Mail Queue Error: Cannot connect to database . However I checked all of the connection information and it's correct. Also, adding if (PEAR::isError($mail)) die($mail->getMessage()); produces no errors!