The most useless error message would have to be "Malfunction 54."

As remembered from my third-year design course at University:

In the 1980's, a Canadian company designed a medical computer system called the Therac25 that used low-intensity radiation to treat small tumors in cancer patients. The device consisted of a reinforced lead box of sorts, with a bunch of medical devices inside, the most exciting of which was a radioactive component that was safely stored during most operations, unless the nurse who was operating the machine didn't follow the set procedures.

The most exciting part of all of this was the terminal attached to the device that controlled all of the functions, from simple power-ups to timing to the actual treatments.

If the user of the machine did anything wrong, it would come up with the message "Malfunction ##", ## being a two digit number representing errors from the most mundane (power of the machine not being turned on) to the extreme (patient in contact with radioactive materials for WAY too long). To make matters even worse, certain malfunction codes represented more than one type of error. No other information would appear, and the error message could be cleared just by pressing any key to continue.

The most notorious of these codes was "Malfunction 54", a term now notorious in its usage to denote useless error codes.

This error code, in fact, killed approximately six people because the nurses had no idea what it meant. "Malfunction 54" indeed represented a dosage of radiation up to ten times more than the safe limit for any sort of treatment.

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