Recenlty while trying to delete product records, we got the below error.
The quick way to figure out which associated entity’s record could have restricted the deletion of the record, open the 1:N relationship for the entity.
Search for any Parental, Referential Restrict Delete or any System relationship that has Restrict set for Delete action.
In our case it was the System relationship of Product with Opportunity Product
With Restrict Behavior set for Delete action.
Deleting all the opportunity product record allowed us to delete the Product records.
Hope it helps..