“It was a sort of unfortunate concatenation of events,”

A software flaw caused the Mars orbiter failure last November:

Instead, an errant computer command five months earlier had been placed in the wrong location of the computer memory for the spacecraft. That, in effect, implanted a fatal defect in the spacecraft, disabling a safety feature to prevent the solar panels from rotating too far and mangling its ability to communicate with Earth in case of a mishap.

NY Times story here.