Adding a new participant in the Approval Workflow is giving Error after approval is completed.

I added a new participant in parallel to the existing participants in my SOA Compsoite Approval Workflow. The Approval task is getting assigned correctly and the respective users are able to approve or reject the request.

After the request is completed, instead going to the Request Completed status, it gives an error-

ORABPEL-30039

exception.code:30039
exception.type: ERROR
exception.severity: 2
exception.name: Error in routing slip.
exception.description: The type of the first participant in the routing slip is expected to be Participant, but it is null. The routing slip is associated with task 57076c8c-b188-4526-a537-f34d19aed578.