I am working in IBM BPM 8.5 The last time I saw this error was in Teamworks 6! It was thrown upon submission of the coach and the most interesting part is that the instance in question got into a FAILED state--in Teamworks 6 it did not fail the instance.
Has anyone else seen this in IBM BPM 8.5.x? Also, did you also observe the instance to fail? Could it have been related to timeout?