Thanks batzee for your help, your suggestion didn't resolved directly my problem but i'm sure my project packaging is much more cleaner now.
For anyone in the same situation, the issue was that I was injecting both an EntityManager and an EntityManagerFactory in the same DAO.
It looks like Jboss and Glassfish have a different implementation for this particulary case.
[Message sent by forum member 'tibill']
http://forums.java.net/jive/thread.jspa?messageID=476667