If you have tried creating a “1:N” relationship between a system entity and custom entity with the "Type of Behavior" property set to “Parental”, you most probably have also gotten an error when you try to save the system entity after updating its parent.
Let’s consider a Contact entity and a custom entity called Specialization. The relationship between Contact and Specialization is a “1:N” relationship with the "Type of Behavior" property set to “Parental”. Contact being a system entity already has a “1:N” relationship with the "Type of Behavior" property set to “Parental” with the Account entity.
So when you try to update the Contact's Parent Customer attribute and save, you are re-parenting the Contact. Since you have a relationship with "Type of behavior" set to “Parental” between the Contact and Specialization, CRM tries to re-parent the Specialization record with the updated Account object which it doesn't find. Hence the "no attribute" error.
To fix the issue, change the relationship between the Contact and the Specialization to “Configurable Cascading” and set the Re-Parent property to "Cascade None"; Save and Publish and your all set.
Now if you try to re-parent the Contact, CRM won’t try to re-parent the specialization record since the Re-Parent property is set to "Cascade None".
