Field Service Error: There are resource requirements related to this record. Please remove resource requirements before deleting this record.
This week i had came across the above error when i was deleting a set of work order records in a clients test system.
Even though the work orders had not been scheduled, it seems that the associated records created for the work orders have been set using the restrict delete behaviour. Annoying but fair enough.
Deleting the Resource Requirements records for the work orders allowed me to delete the Work Orders.