I installed and configured FOSUserBundle, SonataAdminBundle, SonataUserBundle, SonataMediaBundle correctly as written in here http://tech.dupeu.pl/2013/07/symfony-2-3-sonataadminbundle-sonatamediabundle-sonatauserbundle-and-fosuserbundle-a-good-project-base/ and with some research it's fine and I already can create a user, a superadmin etc..
Also Media ans Groups features works correctly ! I have a problem when tryin to add a user in the Admin Dashbord, I donnow exactly what it is about .. I searched on forums and on stackoverflow and it seems that it has a relation with SonataIntlBundle so I reinstalled it and I activated intl extension in my WampServer (Windows 8) but it's not working anymore ..
This is the error ( FatalErrorException: Error: Class 'ResourceBundle' not found in C:\wamp\www\project\vendor\symfony\symfony\src\Symfony\Component\Intl\ResourceBundle\Reader\BinaryBundleReader.php line 32 )
Solved
I fixed the problem by installing symfony/intl with composer : I added this "symfony/intl": "2.6.*@dev" to requiere section then I lunched the composer update command and now it's working !
You can check this link http://symfony.com/doc/current/components/intl.html for more informations!