Another possible bug is bug in class com.arjuna.ats.internal.jta.transaction.arjunacore.jca.TxImporter. There is one field private static HashMap _transactions = new HashMap() TxImporter is used by com.arjuna.ats.internal.jta.transaction.arjunacore.jca.XATerminatorImple. The field is static and there can be more XATerminatorImple objects in JVM or there can more threads in one XATerminatorImple object. The access to that field is not synchronized. Pavel View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4129589#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...