“In a screening room at network headquarters in New York, two CBS vice presidents watched the show in silence. ‘Neither of them laughed once,’ Mendelson recalled. ‘When the lights came on, the executives shook their heads and shrugged. “Well,” said one, “you gave it a good try.” “It seems a little flat,” said the other. “Too slow,” said the first, “and the script is too innocent.” “The Bible thing scares us,” said the other.’ The animation was crude — couldn’t it be jazzed up a bit? The voice talent was unprofessional — they should have used adults. The music didn’t fit — who ever heard of a jazz score on an animated special? And where were the laughs?'”
The show was A Charlie Brown Christmas, the most successful special in television history.
From Schulz and Peanuts: A Biography by David Michael.