Thanks for your reply. anonymous wrote : This looks like a recursive write. Are you trying to use HashMaps as trees? Actually I do not have Maps of Maps if that's what you mean. The "candidate" for this Serialization problem seems the following map (which is the field of a SFSB): TreeMap<SimpleValue, List<Item>> map where SimpleValue is a simple object with two string fields and Item is a quite complex EntityBean among which fields there are also 5 collections. @Entity | @Table(name="item") | public class MItem implements Serializable The objects in these collections may have back references to the item itself. e.g. Item has a ManyToMany relation with the Property object, so each item has a list of properties | @ManyToMany | @JoinTable(name = "item_prop", | joinColumns = {@JoinColumn(name = "ip_item")}, | inverseJoinColumns = {@JoinColumn(name = "ip_prop")}) | List<Property> properties | and each Property has a reference to a list of parent items | @ManyToMany(mappedBy = "properties") | List<Item> items | anonymous wrote : What operation where you performing? The bug, as far as I know from the logs, has been seen twice: - once, as explained above, the user logged out from the webclient since 20 minutes (so nomore stateful beans around to passivate) and the only process turning was a set of stateless beans that polls rpcs messages received from wireless devices. in this case my question is: when does serialization come into play? - second time the user was loading (readonly) the jsf page backed by the bean that I described to see values updates. The TreeMap contains a list of agenda items, and the keys of the map are just some string formatted dates (e.g. key::Day , values::agendasOfTheDay). The TreeMap is used to load the agendas of the day when the user selects the day from a selectMenu and refreshes the page. Hope you can give me some further support.. Thank you, cheers Andrea View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4165085#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...