title: date_diff() expects parameter 1 to be DateTimeInterface, string given
body: <p>They have the same format:</p>
  <pre><code>$date_expire = '2014-08-06 00:00:00';
  $date1 = date(&quot;Y-m-d G:i:s&quot;);
  $date2 = date_create($date_expire);
  
  $diff = date_diff($date1, $date2); //this line makes error.
  </code></pre>
  <p>But I am getting this error:</p>
  <blockquote>
  <p>date_diff() expects parameter 1 to be DateTimeInterface, string given</p>
  </blockquote>