Factual error: 1-11: I Married a Mind Reader. A nitpicking mistake, but on the set of "I Married a Mind Reader", the front door is a modern steel design. Back in the 60's, front doors were almost always wood (steel doors weren't available until the 1970's or 80's), and the window design would have been larger on a 1960's fan-window wooden door.
Continuity mistake: In Episode 411, "Lady Killen": When Lee Scanlon is in Sensai and the janitor walks him to the kitchen, the doors are push-through doors with no handles on them and with circular windows in them. But when they walk through, the doors are not push-through any more, but have handles on the one side they opened with, and no windows.
Revealing mistake: In the first scene of episode 1-15: "Penny for Your Thoughts," the clock shows an impossible configuration. The hour hand is slightly before the five, and the minute hand is between one and two. If it's about seven minutes after the hour, the hour hand should be slightly past one of the other numbers, not slightly before it.
Continuity mistake: Bridget doesn't seem to be aging as she should. In the first season Joe and Allison talk about their '6 year old' and she doesn't have any friends, Ariel is 9 and Marie is a baby. Rolling on to season 4 - Ariel is 14/15, Bridget is 9 (the episode when she's talking to the credit card guy Mr Reshmi - Joe tells him off for speaking for 10 minutes to a 9 year old). So, my point is - it appears five years have passed - Ariel has gone from 9 to 14/15 and Bridget is 9 - that's only 3 years. Marie was approximately a year old or so in the first season and appears to be 3 or 4 in season 4. It would make sense if Bridget were only 4 in the first season and five years later would be 9 but she's mentioned as being a six year old when the teacher tells Joe and Allison that she doesn't have any friends at school and then meets Bobby Le Shell. Please correct me if I'm wrong as I'd love to hear an explanation for this.
Continuity mistake: Episode 6.4, Libra Slayer: In the opening scene, in the hospital, the man leans over the dying patient to hear what he has to say. His cheek is almost touching the patient's lips. Then the angle changes and their faces are suddenly quite far apart.