Class TaskForm.java. If condition defined in the try block checks formButton an instance of CancelButton? If condition is true, then outcome is set to "cancel". | public void processAction(ActionEvent actionEvent) throws AbortProcessingException { | | ..... | | try { | if (formButton instanceof CancelButton) { | | //formButton.setDisabled(true); | log.debug("Cancel button was pressed"); | outcome = "cancel"; | if (creationLogsVar != null) { | requestMap.put(creationLogsVar, Collections.EMPTY_LIST); | } | commit = true; | return; | } | } | | ... | } | In the view.xhtml by <jbpm:outcome custom tag, there is a redirect. Task instance id query parameter is not submitted due to this redirect after a user click the cancel button. Therefore the custom tag which is responsible for rendering the process image tag throws NullPointerException. | <jbpm:outcome outcome="cancel" type="redirect"/> Url of Task Instance View page before cancel button is clicked: http://localhost/main/task/view.html?tiid=11863 Url of Task Instance View page after cancel button is clicked: http://localhost/main/task/view.html I managed to solve the NullpointerException problem by changing the type to "stay". Still I don't know what is the purpose of cancel task form button? Is this cancel button for stopping a process which you started? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4048968#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...