pitosalas, it looks like the Hibernate session is closed and the parent entity you are trying to update, became a detached entity. So you have two ways out:
- Attach an entity to the Session, as described here. Then you need to initialize lazy collections as is mentioned here. After that you can do the update.
- Try to span the lifetime of the Session from the moment you load the entity till the moment you update it. So probably the approach "Hibernate Session per HTTP request" will not work for you, and you will need "Hibernate Session per HTTP session" (see the way it is implemented in Spring Web Flow; you may get some ides from here as well).