how can I force a DC demotion?

I have two domain controllers for a single domain. I need one of them to be Demoted due to a DNS look up failure. The machine I will be demoting has a invalid DNS name for the existing domain and I need to remove it from DC staus. I have used the DCPROMO tool and it returns a error when it tries to demolish AD. Can I force a DEMOTION? If so do I have to do it in active Directory restore mode?
~Brian~