Worker information is missing or not valid.
The Task does not have a field that holds the Known Worker information, the Worker information specified is invalid, or the specified Worker does not exist in TaskRouter.
Ensure the Task field referenced in the Workflow definition is provided in the Task's attributes. If Worker information is provided, make sure that the Worker does exist in TaskRouter. Find out more about the Known Worker Routing feature here: https://www.twilio.com/docs/taskrouter/workflow-configuration/known-agent-routing