An unhandled exception occurs in a step that has no boundary error event handler associated with it. The BPMN implementation is created in a way that process instance execution must be completed even with errors in the instance. The process designer has to consider the various error conditions and design the process model accordingly.

However, most error conditions cannot be anticipated and when a process step fails, that step may be required to run again. When this happens, the step must be restarted. To allow step restart, the process instance must be blocked in case of an unhandled error.

When an exception occurs and there are no error handlers in the process model, the exception is an unhandled exception. In this case, the step status is changed to Failed and the process instance status is changed to Blocked. You restart a blocked instance using Dynamic Business Orchestrator services from the webMethods Business Console user interface. A blocked process instance is still considered Running.