I installed the YooTheme master template (yoo-master2) and activated it directly. The only thing I got was a blank page. I had to remove the template folder to get the default template back again and started debugging.
The following error was thrown:
PHP Fatal error: Class 'DOMDocument' not found in /var/www/mysite/current/public/wp-content/themes/mytheme/warp/src/Warp/Dom/Document.php on line 15, referer: http://www.mysite.nl/wp-admin/update.php?action=upload-theme
The problem was that PHP’s xml library was not installed on my VPS. To install it I had to run:
yum install php54w-xml