Failure of a communications link in an Atlanta computer system for filing flight plans delayed hundreds of flights across the US. The other flight-plan facility in Salt Lake City tried to take up the slack and handle the entire country, but the backup system overloaded. This led to manual processing.
The FAA said that it had never experienced a computer problem this severe.
See, "U.S. airports back to normal after computer glitch," Reuters, Aug, 26, 2008, at http://www.reuters.com/article/topNews/idUSWBT00961720080827