You cannot delete the component because it is referenced in work definition Main for the item

Summary:

Getting an error message when running a Delete Group that 'You cannot delete the component because it is referenced in work definition Main for the item'. I'd done this previously for a different item structure and the component was deleted from structure and the Work Definition updating accordingly after running the 'Process Item Structure Changes to Work Definitions' ESS job. The only difference that I can see is in the case where it worked no Work Order had been created from that WD but in this case one has been created and transacted against. Any ideas as