User blog comment:Thornclaw Braveheart/Witch-king of Angmar vs. Eragon Bromsson/@comment-2006360-20111130020550/@comment-181289-20111130021318

Brisingr can't penetrate all wards, there are several times in the books where it is deflected by wards, one's made by normal men, but the Witch-king is protected by "wards" of Sauron, a Maiar.