Updated rocket design needed updated control theory, but a case was missed, so it went into a roll oscillation, exhausted hydraulic fluid, and then lost control.
See the video description
In 1998 Boeing debuted the new Delta III rocket with a payload demonstrating the larger capacity of the latest evolution of the Delta series rockets. However 72 seconds into the launch the vehicle was lost. The reason for the failure boiled down to a guidance system which used up the limited guidance capability of the strap on solid rocket boosters and ultimately lost control. Lots of data was taken from Boeing’s Delta III Payload guide. Also Ed Kyle’s history of the Delta III provides lots of good links.
and also the short text article:
Boeing Pinpoints Delta III Failure