I recently tried to remove an OU from my Test AD came and up against this message: You do no have sufficient privileges to delete xxxx or this object is protected from accidental deletion.
To get round this I followed this procedure.
- Ensured Advanced Features was selected in AD Users and Computers.
- Selected the OU, the Properties and then Security.
- Clicked the Advanced button.
- Removed the Deny option from the Everyone group.
I was then able to delete the OU.
More info: https://technet.microsoft.com/en-us/library/cc736842(v=ws.10).aspx.