Message:You do not have sufficient privileges to delete OU, or this object is protected from accidental deletion.

1. Open Active Directory Users and Computers.
2. Click on View then click on Advanced features.
3. Right-click on the OU and select Object ta
4. Uncheck the option Protect object from accidental deletion
   
5. Remove the OU.

Remark: If this OU has AD objects under it, you will not be able to remove it if one of the objects is protected against accidental deletion.

Is a very simple solution.