Protecting Container from Accidental Deletion is enable by default when the OU is created

Protecting Container from Accidental Deletion is enable by default when the OU is created. The option can be viewed in the new OU creation wizard.

To remove the protection:

1. Enable the Active Directory Users and Computers advanced feature view mode

Right click the Domain node in AD users and Computers--->View--->Advanced Features

2. Remove the explicit Deny ACEs for the Delete and Delete Subtree advanced permissions for the Everyone group.

Right click the specific OU--->Properties--->Security--->Advanced--->Everyone--->Edit--->Remove the explicit Deny ACEs for the 'Delete' and 'Delete Subtree' permission