Okay, it seems that under 4.0.5 I had been ignoring warnings like these: 20:35:12,718 WARN [TxConnectionManager] Prepare called on a local tx. Use of local transactions on a jta transaction with more than one branch may result in inconsistent data in some cases of failure The TX service in 4.2 treats this condition as an error. As an experiment, I changed the EJB3 timer to use MySQL 5.0, as described by the following: http://wiki.jboss.org/wiki/Wiki.jsp?page=SetUpMysqlAsDefaultDS But I still got the same error. Further investigation revealed that I get this error if I attempt to call an async method having previously done anything "EJB" (say, select something) in the same method. The only solution I could find was to separate out the calls of the required concerns: JSF ManagedBean -> A:doSomethingEjb(); JSF ManagedBean -> B:callAsyncMethod(); There is no mention of this potential trap in the reference guide - might be useful to add something? BTW - I found this to be a concise souce of info with regard to understanding what 2 phase resources are: http://dev.mysql.com/doc/refman/5.0/en/xa.html Cheers, C. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4049560#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...