PHP : Fatal error: Call to undefined function

require 'lib/script.php';
$categorie = liste_categorie();

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in 

$categorie = liste_categorie();
while($ligne_categorie = mysql_fetch_array($categorie))
{
echo '<li><a href=index.php?categorie='.$ligne_categorie['id_categorie'].'>'.$ligne_categorie['nom_categorie'].'</a></li>';
}

function liste_categorie()
{		
$MaConnexion 	= new Connexion(CONST__host, CONST__name, CONST__pass, CONST__base_carre_alizes);
$tab 	 	 	= array();
$tab 	 		= $MaConnexion->select('SELECT * FROM categorie ORDER BY nom_categorie ASC');

if ( $MaConnexion->getNbLignes() > 0 )
{
return $tab;
}
else
{
return 0;
}
$MaConnexion->__destruct; 
}