Additional uncaught exception thrown while handling exception.

<h1>Additional uncaught exception thrown while handling exception.</h1><br />
<b>Fatal error</b>:  Uncaught Error: Class &quot;Drupal\Component\Utility\Html&quot; not found in /home/platzhirschfulda/public_html/core/lib/Drupal/Component/Render/FormattableMarkup.php:238
Stack trace:
#0 /home/platzhirschfulda/public_html/core/lib/Drupal/Component/Render/FormattableMarkup.php(211): Drupal\Component\Render\FormattableMarkup::placeholderEscape('Symfony\\Compone...')
#1 /home/platzhirschfulda/public_html/core/lib/Drupal/Component/Render/FormattableMarkup.php(78): Drupal\Component\Render\FormattableMarkup::placeholderFormat('%type: @message...', Array)
#2 /home/platzhirschfulda/public_html/core/includes/bootstrap.inc(144): Drupal\Component\Render\FormattableMarkup-&gt;__toString()
#3 /home/platzhirschfulda/public_html/core/includes/bootstrap.inc(126): _drupal_exception_handler_additional(Object(Symfony\Component\DependencyInjection\Exception\RuntimeException), Object(Error))
#4 [internal function]: _drupal_exception_handler(Object(Symfony\Component\DependencyInjection\Exception\RuntimeException))
#5 {main}
  thrown in <b>/home/platzhirschfulda/public_html/core/lib/Drupal/Component/Render/FormattableMarkup.php</b> on line <b>238</b><br />