Error after Site Move

i moved my elgg installation to a new server ( i followed everything in this tutorial

I can correctly view the site(except for users avatars),access to it, but when i run upgrade.php i get the following error :

Fatal error: Call to undefined function _elgg_get_site_secret_strength() in /var/www/mysitedir/engine/lib/upgrades/2013060900-1.8.15-site_secret-404fc165cf9e0ac9.php on line 9

What should i do?