PHP - Consulta principiante

Hola, estoy recien metiendome en PHP y me pasaron una página y me da el siguiente error:
Warning: realpath() has been disabled for security reasons in /funciones/template.php on line 25
y parte del codigo de la pagina template.php dice:

<?php

/*

SmashTemplate

A very simple template class. It loads a template from
a file, converts placeholders into php code, then
evaluates the code. Replacing variables in this manner
allows for the usage of php code in the template. This
makes templates more flexible.

*/

class template
{
var $contents; // holds the contents of the loaded template
var $variables = array(); // holds set variables
var $templatedir; // the directory containing templates.

// Sets template directory

function template($templatedir)
{
$templatedir = realpath($templatedir); ***** acá me da el error ****
$this->templatedir = $templatedir;
}


a qué se debe este error?

Gracias.