By default PHP does not show notices that often can be signs of greater problems.

Why Enable E_NOTICE?
How?
# Inside PHP.ini
error_reporting = E_ALL

# Inside httpd.conf or .htacess
php_value error_reporting 2047

# Inside a script
<?php
ini_set("error_reporting", E_ALL);
/* or */
error_reporting(E_ALL);
?>