Human error caused the loss of MGS
The "computer error" was in fact human error:
A command sent to the wrong computer address caused a cascade of events that led to the loss of the Mars Global Surveyor spacecraft in November, NASA investigators reported Friday.
The error by ground controllers in Denver caused the spacecraft to mistakenly think its solar panels were stuck. By trying to free them, one of its onboard batteries overheated, eventually causing a loss of power.
Here
Another black eye for NASA. The fact MGS was many years past it's primary mission should not be an excuse. It was still an extremely valuable asset.