Fatal error: Uncaught Error: Call to undefined function wp_installing() in /var/www/wp-content/plugins/wordpress-seo/wp-seo-main.php:421 Stack trace: #0 /var/www/wp-content/plugins/wordpress-seo/wp-seo.php(50): require_once() #1 /var/www/wp-settings.php(517): include_once('/var/www/wp-con...') #2 /var/www/wp-config.php(107): require_once('/var/www/wp-set...') #3 /var/www/wp-load.php(50): require_once('/var/www/wp-con...') #4 /var/www/wp-blog-header.php(13): require_once('/var/www/wp-loa...') #5 /var/www/index.php(17): require('/var/www/wp-blo...') #6 {main} thrown in /var/www/wp-content/plugins/wordpress-seo/wp-seo-main.php on line 421