Factual error: In the scene about driving to the guest house in Rodanthe, Dr. Flanner is depicted crossing a large bridge after taking a ferry. This is impossible. There is no large bridge of any kind between the ferry on the southern coast of Hatteras Island and Rodanthe, located to the north, mid-way on the island. The bridge shown was actually the Herbert C. Bonner Bridge, a two-mile span connecting Hatteras Island to the northern Outer Banks, which is the direction the character was headed, meaning he went past Rodanthe several miles earlier. Maybe he missed it in the fake sand storm.
Factual error: The doctor parks his car under the house before the storm hits. Since the house is on the beach and the wind and water hit the house, there is no way his car would start and be so clean after such a storm.
Other mistake: When they go up into the attic to look at the art, it seems as though the candle is already burning when they get up there.
Factual error: The scene in which the wild "banker" ponies run by the main heroine and her friend could not have taken place in, or anywhere near, the Hatteras Island village of Rodanthe. There are no wild horses on Hatteras Island. To see wild horses on the Outer Banks of North Carolina, one needs to leave Hatteras Island and travel sixty miles north to Bodie (pronounced 'body') Island and the beaches near the village of Corolla (pronounced 'cor-allah'), or south fifty miles to Ocracoke Island and the pony pens administered by the National Park Service.
Continuity mistake: It appears the scene Diane Lane has with Paul's son Mark at her home was filmed at a different time in Diane's life. Her hair is a different color and style and her face looks older. Looks like she had some work done on her face. But then the scenes following, when kids come home and Diane is depressed from Paul's death, she looks like she did at beginning of the movie.