Fatal error: Call to undefined function mysqli_connect() in /home/user/public_html/includes/connection.php
MySQL Improved extension was disabled in hosting environment.
This error was fixed by enabling the MySQL Improved extension and recompiling the Apache via EasyApache.
The MySQLi extension is an improved version of the older PHP MySQL driver used in the PHP to provide an interface with MySQL databases. To enable Improved extension from WHM, refer to following knowledgebase article.