This error occurs because a site has been moved and the database on the new server contains information about plug-ins that are not installed on the new server.

If this happens when trying to edit an article:

  1. Locate the following code around line 260 in libraries\joomla\html\editor.php

// Try to authenticate -- only add to array if authentication is successful

$resultTest = $plugin->onDisplay($editor);

if ($resultTest) $result[] = $resultTest;

and change it to

// Try to authenticate -- only add to array if authentication is successful

if (method_exists($plugin, 'onDisplay')) {

$resultTest = $plugin->onDisplay($editor);

if ($resultTest) $result[] = $resultTest;}