I get the same error whenever I try to list tasks or processes in the console using JBPM 5.3. I have tried upgrading to JBOSS 7.1.1 as per Timothy's solution but still get the same result.
My installation of JBPM 5.3 is a 'vanilla' install in to JBOSS AS.
I see another post https://community.jboss.org/message/743095#743095 referencing the same error.