Yet another case of human boo-boo sent a spacecraft into oblivion. At least that was the conclusion of NASA in its investigation of the loss of the Mars Global Surveyor, which was lost in November 2006.
Operators at the NASA facility in Denver apparently sent a wrong command on the spacecraft's computer, causing it to eventually lost power. The command, which is for orienting the satellite's main antenna, was sent to the wrong address, causing the spacecraft's batteries to overheat, leading to the loss of power that shut down the MGS.
MGS was launched in 1996 and was responsible for many findings made about Mars, including the evidence that waters still flows in the Martian surface.