When you try to open your site you can get an error 500 or your site works incorrectly (returning random errors). It can be caused by Zend OPCode Cache, eAccelerator or xCache applications on your server. Mentioned applications conflict with our templates.
If you want to make sure that Zend OPCode Cache, eAccelerator or xCache are enabled on your server you should uploaded attached php_info.php file to your template folder on your server and open this files in your browser using link like this one: http://yourdomain.com/php_info.php
If you scroll down this page you'll see if Zend OPCode Cache, eAccelerator or xCache are enabled on your server:
In order to solve this issue you should contact your hosting provider and kindly ask them to disable Zend OPCode Cache, eAccelerator, xCache.
Also you can try to disable it by adding following line in your .htaccess file:
php_flag opcache.enable Off