Configuration file config.ini can't be loaded

<?php

use Phalcon\Mvc\Application;
use Phalcon\Config\Adapter\Ini as ConfigIni;

try{
    define('APP_PATH', realpath('..') . '/');
    $config = new ConfigIni(APP_PATH . 'app/config/config.ini');
    // ......

Hi,

sorry to bother you. I have the error "Configuration file config.ini can't be loaded" while the file path is correct. Do you have any idea. FYI I'm using Phalcon 2, CentOS 7, PHP 5.4

thanks in advance,

update

the cause of the error is located: I use the word "on" as a name of a key (like: on = TRUE). if anyone can provide more prohibited name, I am willing to give points to you.