Factual error: When Rob climbs up the elevator shaft, he comments on how greasy it is, and when he jumps back into the elevator, he wipes his hands on his shirt but not a bit of grease shows on his clean white shirt.
Character mistake: Rob tells the people that are about to get on the elevator "my wife is expecting a baby!" In all the other episodes where "she's expecting a baby" as well... No change in stomach size at all! Not a single sign of pregnancy... (After 12-16 weeks it starts to show that the baby is there.) Even before Richie was born, still flat as a pancake.
Other mistake: After Lyle gives back Rob and Laura's watch's and the $51, Rob doesn't get his ring back.