Mars Polar Lander: Clues From the Crash Site

"As one of NASA's faster, better, cheaper missions, the Mars Polar Lander project lacked in realistic tests, Slostad explained. And when the lander's multiple instruments were operated simultaneously in pre-launch tests, the spacecraft's central processing unit would sometime start to bog down. 'It would either slow way down, freeze, or just crash,' he said."

Yeah, that might be a problem.