Problem with Pegasus booster - not with the X-43A
X43-A Hypersonic Test Vehicle Destroyed During Test Flight
[2 June 2001] NASA was forced to destroy its X43-A hypersonic test vehicle today over the Pacific Ocean when its Pegasus launch vehicle veered of course. The test was being staged from Edwards Air Force Base in California. While no final cause has been identified for the malfunction, preliminary indications point to problems with the Pegasus booster - not with the X-43A.
http://www.spaceref.com/news/viewnews.html?id=356