EntryInfo ei = Entry.GetEntryInfo(17, LFSession);
                    FieldValueCollection fvc = ei.GetFieldValues();
                    fvc.Add("TestField", "Chicken Parm");
                    ei.Lock(LockType.Exclusive);
                    ei.SetFieldValues(fvc);
                    ei.Save();
                    ei.Unlock();
                    ei.Dispose();

This code does not work. It produces the error, "Message: Field not found. [9016]". Does the field "TestField" have to already exist somewhere? Do I need to create the field with code before I add it?