We are using JBOSS 6.3 EAP and  its throwing below error some times.  But after restarting JBOSS Applcation server couple of times, it will get work fine.

Kindly help us on this and how to resolve this error.

JBWEB000236: Servlet.service() for servlet WorkflowServlet threw exception: java.lang.IllegalStateException: JBWEB000212: Session already invalidated