Hi John
Process Controls is not my background, however, could this error be restricted from your IMG configuration for entity level authorisations?
You could try to run ST01.ST05 traces for authorisations and SQL to identify what is being checked just prior to the error message.
Here's some SAP help overview for it (I suspect this is what Fernando was referencing). If not search for Entity Level Authorisation for Process Controls to find the overview.
Regards
Colleen