PHP代码-返回错误

我正在尝试在首先检查sql查询后自动处理电子邮件警报。

由于我对php不太熟悉，我找到了一个用于此目的的代码，但第29行返回了一个错误。

   while($row = mysqli_fetch_array($result))
  {
  $message = {$row['User Name'] . " " . $row['Email']. " " . $row['Course']. " " .      $row['Attempt']. " " . $row['Grade']. " " . $row['Finish time']'n};
  }

请告知。你可以在下面找到所有的代码。非常感谢。

<?php
$con=mysqli_connect("localhost","user","pass","db");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }
$result = mysqli_query($con,"SELECT
us.username AS 'User Name',
us.email AS 'Email',
qu.name AS 'Course',
quat.attempt AS 'Attempt',
quat.sumgrades AS 'Grade',
FROM_UNIXTIME(quat.timefinish,'%M %D %Y %h:%i:%s') AS 'Finish time'
FROM mdl_quiz_attempts AS quat
JOIN mdl_user AS us ON quat.userid=us.id
JOIN mdl_quiz AS qu ON quat.quiz=qu.id
WHERE (quat.attempt = 3 OR quat.attempt = 6) AND quat.sumgrades < 80 AND quat.timefinish > (unix_timestamp(now())-300)
ORDER BY us.username,qu.name,quat.attempt");
if($result->num_rows>=1) {
   $email='dc@antaea.com';
   $subject = "E-School failed attempts";
   $message='One or more users failed quiz three or more times:'n'n';
   while($row = mysqli_fetch_array($result))
  {
  $message = {$row['User Name'] . " " . $row['Email']. " " . $row['Course']. " " . $row['Attempt']. " " . $row['Grade']. " " . $row['Finish time']'n};
  }
  if(mail($email, $subject, $message)) {
      //mail successfully sent
   } else {
      //mail unsuccessful
   }
}
mysqli_close($con);
?>