DACS blamed for MCI / CSX train problems last week

[Sean Donelan <sean () donelan com>]

According to Computerworld, the MCI outage affecting CSX rail lines
last week was caused by DACS problems.

http://www.computerworld.com/home/print.nsf/all/000505DCCE

This isn't the first DACS problem nor is MCI the only carrier affected
by DACS problems.  Bell Atlantic had a multi-day DACS problems, I've
experienced 18+ hour MCI DACS problems in the past.  What is it about
DACS systems which seem to lead to such catastrophic problems?  How
can you put an entire train system out of operation due to a single
piece of equipment?