I had a record in an object named ArrangementType. This record is currently tied to a Project record instance, which has the ArrangementType as a required attribute.
The relationship is was set to "peer" between the 2 objects
I tried to delete the ArrangementType record, and got an error that it could not locate the associated record in Project. I was not trying to delete the record in Project, so I am confused on that.
I then changed the Project.ArrangementType attribute to not required. I was then able to delete the Arrangement record, and it left that attribute null in the existing Project record instance.
So, it seems that there is some guard against deleting records in a Object which has been referenced in another object, IF that other object has set that referenced attribute to "required".
I guess I am most confused about the delete error message on the ArrangementType record.