Factual error: Day 22 and day 67 are both on Sundays, which does not add up.
Other mistake: When Ted and Robin borrow Marshall's Fiero and are sitting in the car talking as Ted drives, you can hear the beat of a song playing in the car that is not the Proclaimers' I'm Gonna Be (500 Miles), which in many future episodes is referenced as the only song that can be played in that car due to the tape being stuck in the tape player. (00:15:30 - 00:16:10)
Suggested correction: Maybe it's on the radio.
Continuity mistake: When Robin and Ted are at the bar planning their weekend away together, the level of beer in the glass next to them goes up and down between shots. (00:10:00)
Continuity mistake: In the scene at the hotel bar, the red straws lying on the table next to Ted change position between shots without being touched.
Continuity mistake: In the scene at the bar where Robin is describing looking after Marshall as being like having a baby, Barney's drink moves from in his hands to on the table and back again instantly between shots. (00:06:30)
