A computer glitch, that was discovered more than a year earlier, caused the backup system to fail on the FAA computer. This caused a 3 hour shutdown of radar systems at the Los Angeles Air Route Traffic Control Center in Palmdale California.
The Voice Switching and Control System (VSCS), originally on Linux, upgraded about a year ago to Dell computers using Microsoft software. The Microsoft software contained an internal clock designed to shut the system down after 49.7 days to prevent it from becoming overloaded with data. Analysts said a shutdown mechanism is preferable to allowing an overloaded system to keep running and potentially give controllers wrong information about flights.

The agency’s radio system in Palmdale shut itself down on the afternoon of Tuesday September 16, 2004 because a technician failed to reset and internal clock - a routine maintenance procedure required every 30 days by the FAA. Then a backup system failed, also as a result of technician error, officials said. (#1)

The radio failure rippled throughout the nation’s airports, grounding hundreds of commercial flights and forcing conntrollers working from other centers to divert hundreds more to locations outside Southern California.
Los Angeles International Airport officials said about 30,000 passengers were affected, with 500 or spending the night in the terminals. The backlog of incoming flights was not cleared until 3am Wednesday. At LAX, 450 flights were diverted or cancelled and another 150 were delayed. An additional 32 were cancelled Wednesday morning because the aircraft did not arrive Tuesday night.
Other airports - Ontario, Bob Hope, John Wayne, Long Beach and Palm Springs, as well as San Diego - experienced significant delays, and airports throughout the West took diverted flights.

There was a loss of radar system for 178,000 square miles, thoughout California, to Arizona and Nevada. (#1)