Hi,
When using Seam with EJB3, obviously the way is:
@PersistenceContext(type=EXTENDED) private EntityManager em;
I think you must use a Seam Managed Persistence Context (SMPC). Actually, I think this is the preferred way even when using EJB3
http://docs.jboss.com/seam/2.0.0.B1/reference/en/html/persistence.html#d0e5466