NASA - Darkness as Dawn goes on hold
NASA ordered the Discovery class Dawn mission to stand down for its 2006 launch.
ie they are to put launch on indefinite hold.
Sounds like there were some technical issues, but unless someone ain't telling, they sound like "normal difficulties".
Real problem seems to be NASA cuts and JPL cuts in particular.
Dawn is an ion engine propelled mission to the asteroids Ceres and Vesta.