Metodo _toString() Doctrine, Service

[pmeninsaxmus16]

Hola a todos tengo este error:
The Response content must be a string or object implementing __toString(), "object" given.

porque estoy haciendo una consulta en un service que es asi:

+++++++++++++++++++++++++++++++++ service
function __construct($entityManager, $container)
{
$this->em = $entityManager;
$this->container = $container;
}
function generarIdCarStudent($id)
{
$sql2="SELECT a.firstname FROM ABCIsystemBundle:AbcMembers a where a.id='$id'";
$query2= $this->em->createQuery($sql2);
$query2->getResult();
return $query2;
}
+++++++++++++++++++++++++++++++++

y en e controller lo llamo asi

================================== controller
{

$prueba= $this->get('applicantAdmission');
$msg=$prueba->generarIdCarStudent($id);
return new Response($msg);
}
=======================================

alguna ayuda