NASA investigatators investigating the Taurus XL launch failure carrying its Glory environmental monitoring mission disclosed that the fairing nose cone did not separate due to its rail not breaking as planned.  However, they could not work out why this happened.  The full story is available here:

http://sdv2.uk.w3pcloud.com/news/articles/nasa-unable-to-explain-taurus-xl-fairing-failure-382621/