Php – require_once :failed to open stream: no such file or directory

I have this testing code in "PAGE A":

<?php
require_once('../mysite/php/classes/eventManager.php');
$x=new EventManager();
$y=$x->loadNumbers();
?>

"eventManager.php" has inside a require_once:

<?php
require_once('../includes/dbconn.inc');
class EventManager {...}
?>

My folders structure is this:

mysite/php/classes folder and includes folder

If i test PAGE A in a browser i receive:

Warning: require_once(../includes/dbconn.inc) [function.require-once]: failed to open stream: No such file or
directory in C:\wamp\www\mysite\php\classes\eventManager.php on line
3

---

Fatal error: require_once() [function.require]: Failed opening required '../includes/dbconn.inc' (include_path='.;C:\php5\pear') in
C:\wamp\www\mysite\php\classes\eventManager.php on line 3

where is the error?

Thanks
Luca