Configuración archivos Mongodb con errores de conexión

$config['mongo_server'] = 'localhost:27017';
$config['mongo_dbname'] = 'ar';

//mongodb host
$config['default']['mongo_hostbase'] = 'localhost';
//mongodb name
//$config['default']['mongo_database'] = 'linkexchange';
$config['default']['mongo_database'] = 'ar';
//mongodb username - by default, it is empty
$config['default']['mongo_username'] = 'root';
//mongodb password - by default, it is empty
$config['default']['mongo_password'] = 'root';