If the BPM connector is being used in combination with an XA transaction, marking a SendMuleEvent action to do an async send results in the XA transaction not working properly, the Worker Thread does not send the message in a transactional context. If you instead attempt to use send mule event marked synchronous, the resulting outgoing message, for instance a JmsMessage is attempted to be stored in Jbpm as the INCOMING_DATA variable. As jms messages are not persistable as workflow state by jbpm, hibernate/jbpm puke when the session is flushed at commit time. There should be an option to do a synchronous "send but dont store incoming" when sending messages from jbpm.