If that helps here is some info from my server error log:
Access Log
2.84.46.143 – – [06/Aug/2014:15:09:13 +0300] “GET /wp-content/themes/cardinal/js/sf-admin.js?ver=1.0 HTTP/1.1” 200 4014 “http://metrax.gr/wp-admin/update.php?action=upgrade-theme&theme=cardinal&_wpnonce=77b01bdcd7” “Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0”
Error Log
[Wed Aug 06 15:14:00 2014] [warn] [client 2.84.46.143] mod_fcgid: stderr: PHP Fatal error: Call to a member function execute() on a non-object in /var/www/vhosts/metrax.gr/httpdocs/wp-content/themes/cardinal/includes/option-extensions/extensions/custom_fonts/extension_custom_fonts.php on line 79