The aircraft that Kevin and Jenna try to fly to Aspen in is shown connected to the airports jet-way. It is a Boeing 737 with blue painted engines.
737's have a 3x3 seating configuration but the interior shots show a smaller aircraft's interior with a 2x2 seating configuration.
When the aircraft taxis and takes off, its engines are now red.
When Jenna and Kevin are discussing the picture of the Winters, Jenna is wearing a ring on her left ring finger, generally signifying engagement or marriage. Not wearing any ring throughout the rest of the movie. Probably a personal item of the actress while filming that failed to be noticed and removed in editing or re-shot.
The position of the $20 bill Kevin showed the attendant at the airport.
When Chris brings in the mail bag he says that Santa Claus, Indiana is the only town named such. There are two other towns in the US named Santa Claus, one in Georgia and a ghost town in Arizona.
The pilot announces the Aspen County Airport is closed. There is no Aspen County in Colorado. Aspen is in Pitkin County and it is the Pitkin County airport.
Kevin says that Aspen is a big town. It isn't. It is a small former mining town of 7000 people.
There are no airports outside of Santa Claus, IN. The closest regional airport is 30 miles away. The closest International airport is located in Louisville, KY, which is over 60 miles away.
When Jenna and Kevin were in their separate rooms, presumably writing their stories, the camera focused on their screens and each time, only a bunch of gibberish is typed out as though the actors were simply pressing the letters J and K multiple times.
When Jenna is unpacking in her room all the lights are on but the light switches are off...
"Rudolph", the Winters car, appears to be a 1941 Plymouth coupe; it wouldn't have the seating capacity to transport four people (Carol, Chris, Jenna and Kevin) from the airport to the inn.