Edit File: upgrade-functions.php
<?php /** * WordPress Upgrade Functions. Old file, must not be used. Include * wp-admin/includes/upgrade.php instead. * * @deprecated 2.5.0 * @package WordPress * @subpackage Administration */ _deprecated_file( basename( __FILE__ ), '2.5.0', 'wp-admin/includes/upgrade.php' ); require_once ABSPATH . 'wp-admin/includes/upgrade.php';