title: PHP error: "Cannot pass parameter 2 by reference"
body: <p>I just need help on this PHP error which I do not quite understand:</p>
  <blockquote>
  <p>Fatal error: Cannot pass parameter 2 by reference in /web/stud/openup/inactivatesession.php on line 13</p>
  </blockquote>
  <pre><code>&lt;?php
  
  error_reporting(E_ALL);
  
  include('connect.php');
  
  $createDate = mktime(0,0,0,09,05,date(&quot;Y&quot;));
  $selectedDate =  date('d-m-Y', ($createDate));
  
  $sql = &quot;UPDATE Session SET Active = ? WHERE DATE_FORMAT(SessionDate,'%Y-%m-%d' ) &lt;= ?&quot;;
  $update = $mysqli-&gt;prepare($sql);
  $update-&gt;bind_param(&quot;is&quot;, 0, $selectedDate);  //LINE 13
  $update-&gt;execute();
  
  ?&gt;
  </code></pre>
  <p>What does this error mean? How can this error be fixed?</p>