Other mistake: In one of the opening scenes with Will and Dr Smith, the Robot's power pack is clearly missing.
Lost in Space (1965)
1 mistake in Welcome Stranger
Starring: Guy Williams, June Lockhart, Mark Goddard, Marta Kristen
Robot: Danger, Will Robinson! Danger.
The Great Vegetable Rebellion - S3-E23
Trivia: Due to their uncontrollable laughter during filming of the infamous "Vegetable Rebellion" episode, Guy Williams and June Lockhart were written out of the next two episodes.