A quick suggestion:
Are you sure your application.xml is correct? Based on what you write, I guess that it should contain 3 modules; 2 ejb and 1 web?? Maybe the persitence ejb module entry is missing...
I figure out the problem,
I pack my project with Maven2 and one of the dependencies was the persistence-api jar
that jar was packed in my ear and it collide with the one already in Jboss lib so i guess that was my problem...
any way i have removed the dependency (made it provided in Maven) and now it is working.
Thanks any way