Prosites 3.5.2 Fatal Error on new update

Hi There,
I've just updated to Prosites 3.5.2 and it triggered the follownig fatal error:

[15-Mar-2016 20:17:35 UTC] PHP Fatal error: Call to undefined function is_user_logged_in() in /usr/share/nginx/skizzar/wp-content/plugins/pro-sites/pro-sites.php on line 1799

Running on the latest version of wordpress.