Continuity mistake: At the end of National Treasure 1, Riley has a Ferrari 360 Spider. At the beginning of Book of Secrets, when his car is being towed away, it's a Ferrari F430 Spider. At the end of the movie, he is given back a 360 Spider.
Factual error: Ben, Abigail and Riley arrive at the Library of Congress to take the President's Book very late at night. However the Library of Congress, despite being shown as open, consistently closes at 5 PM.
Revealing mistake: In the scenes where Riley is using his computer to look up information on the "SearchInfo" site, the screenshot used is of Wikipedia. (You can even see the "About Wikipedia" link on the left).
Ben Gates: Before the Civil War, the states were all separate. People used to say "the United States are..." It wasn't until the war ended that people started saying "the United States is..." Under Lincoln, we became one nation.
Riley: We've broken into Buckingham Palace, stolen a page from the President's super secret book, and actually kidnapped the president of the United States. What are we going to do next, shortsheet the Pope's bed? Ben: Well, you never know.