HI, in order to claim the task, the task has to be in a Ready state, i.e. it has to have the Status.Ready status. See http://hudson.jboss.org/hudson/job/jBPM5/lastSuccessfulBuild/artifact/target/jbpm-5.1-SNAPSHOT-docs-build/jbpm-docs/html_single/index.html#d0e179. You probably tried to invoke the claim operation on a task, that has already been assigned to someone.Please note, that If the task only has one pottential owner(like in the self evaluation process in the jbpm5 demo) it is assigned to him automatically. Try to load the task a have a look at the status attribute.