If you're playing more and more with Group Policy, and I know I am, you'll probably come across an Auditing Policy for the domain controller.
The policy includes the following information:
Why did we do this? Well, you'll have to read my long winded previous post on Error 800423f2. If you look at the bottom of that post, you'll notice how Directory Service Auditing must be disabled. Well, this is how it's disabled. Removing this policy will probably result in a much higher failure rate on your backups.