When Ethan, Iassac, and Chris are going to see Betsy in the hospital and they find Mr. Greens car you can see in the background where they did not completely snow the ground where there should be snow. This film was shot in the middle of August in New York City so all snow had to be created.
When Ethan has dinner at Chris' mother's house, he dials a number on his iPhone, but he actually types it in the calculator app.
When the three of them are running on the snowy street to the hospital and then find the car to borrow, the rest of the street in the distance clearly has no snow.
When they are in Manhattan and getting on the F Train at Church Avenue the location is incorrect. The Church Avenue station is located in the neighborhood of Kensington in Brooklyn, Ny.
The Nutcracker Ball is explained to be a very secretive event, with the new location for the ball each year not being released until 10pm on the night, however at the end of the film, Mr Green explains that he has been holding the event for years in the exact same warehouse.