Can't log after uprade to 3.2 version

More information:

When I reach the login page, I get the next information in Apache Error.log:

[Mon Mar 11 20:33:54 2013] [error] [client 92.56.2.118] PHP Fatal error: Call to undefined function date_diff() in C:\\AppServ\\www\\Proyectos\\model\\Audit.php on line 120, referer: http://XXXXXX/view/main.php


When I get a not succesful login, after that, each time I try to reach the login page I get "ERROR 500" error until I clean browser cache.

The problem is in date_diff function.

If I change the next code:

$audit->lastAccess=date('Y-m-d H:i:s');
$duration=date_diff(date_create($audit->connection), date_create($audit->lastAccess)) ;
$audit->duration=$duration->format('%H%I%S');

To:

$audit->lastAccess=date('Y-m-d H:i:s');
$duration='01:01:01';

It Works!!!

So, the problem is with date_diff function. And I have read that it is not implemented until PHP Version 5.3 and I have installed PHP Version 5.2.17

Could give a fix to this error or must I upgrade my PHP version? I prefer not to do that because I have more php applications on this server...