Fifty-Two, Forty-Five or Work - S5-E13
Continuity mistake: Rob tells Sally, Buddy and Mel "It was rough... Out of work, new house, no furniture, a baby on the way, 1 single dime in the bank!" In several other episodes Rob said they either already had a kid, or they were on their way to the hospital in the cab, on their way to the hospital in the back of a laundry truck, or were already at the hospital. They already had furniture in the other episodes when they brought Richie home from the hospital.
Fifty-Two, Forty-Five or Work - S5-E13
Other mistake: Right at the beginning of this episode Rob says "9 years ago right in this office... I just came on as head writer 2 months was all... Buddy, Sally and I were sitting at this desk, writing a sketch, and you (Mel) came in with some special news." (so on and so forth with that line.) Rob, Sally and Buddy weren't in "this office" building... Didn't even have the same desk or furniture.