Many To Many - persisting entity problem?

[girlcoder]

Hello

Welcome everybody.
I am a new seam user and I really like it, but it is not easy to learn.

Could You please
Help me ? 

with this:

I have two entities  with relationship many-to-many, generated from existing database - Generate Seam Entities (I am using JBoss Developer Studio)
and I could not persist it.
I've been looking for solution for two days...

Exception: javax.ejb.EJBTransactionRolledbackException: org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions

How to make it persist ?

Agnieszka

here is a piece of my session bean:

@Stateful
@Name("newS")
@Scope(ScopeType.SESSION)
@Restrict("#{identity.loggedIn}")


public class NewServiceAction implements NewService {

      @PersistenceContext
      private EntityManager em;
        
     
      @Out(required=false)
      private CbService cbService;
       
      private CbShortCode selectedCbShortCode;       
      private List<CbShortCode> cbShCode;
      

      public void createCbService(){
             cbService = new CbService();                                                  
      }
      

      public void process()
        {
           
          //other cbService attributes set by form on xhtml page

          cbService.getCbShortCodes().add(selectedCbShortCode);     
          
          
          em.persist(cbService);
                    
        }
           
        //data for shortcode selection form on xhtml page 
        @Factory("fcbShCode")
        public List<CbShortCode> getCbShortCode(){
             
             cbShCode = em.createQuery("select s from CbShortCode s order by s.addr asc").getResultList();
          return cbShCode;
             
        }