Castle of Terror
Developed by Beam Software
Written by Grahame Willis
Released in 1985 for Commodore 64
Castle of Terror Spoilers!
From Wikipedia: "The game received notoriety amongst gamers as being impossible to fully complete, namely due to there being no known way to kill the count or achieve a full score of 290 out of 290. Grahame Willis, author of the game, has since revealed that it is not possible to kill the count and that messages suggesting so were placed in the game intentionally to frustrate players."