One of the main causes of failure seems to be making systems too complicated to use. An example of this I found was of the Denver airport baggage handling system. It involved 300 different computers for a start!
This system was actually so complex that the development overrun prevented the airport from opening on time. Fixing the incredibly buggy system required an additional 50% of the original budget which was almost $200 million.
From looking at different failures online and in newspapers, it became clear that some failures came at more than a financial cost. The most extreme example I could actually find was in 1992 when there was a failure to the London Ambulance Service. With a city that has a population of about 8 million, you can imagine how crucial the ambulance service information system is.
After a succession of software engineering failures, especially in project management, 2 failures of London’s (England) Ambulance dispatch system occurred. The repair cost was estimated at £9 million, but it is believed that the human cost was much greater, because people died who would not have died if ambulances had reached them as promptly as they would have done without the failures.
If you want to read more, I found this information at this link: http://bugsniffer.blogspot.ie/2007/11/infamous-software-failures.html