Corrected entry: Hagrid says, when Harry's broom is acting strangely during the Quidditch match, that it's "powerful Dark Magic," and that a student couldn't do something like that. In Harry Potter and the Half-Blood Prince, Hermione uses a simple Confundus hex on Cormic McLaggen, which has a similar, albeit not as great, effect. Point is, while it may have been Dark Magic, it is still possible to do with hexes and jinxes.
Corrected entry: In Harry Potter and the Philosopher's Stone we are told that James Potter (Harry's father) was made prefect when he was in Hogwarts, but in Harry Potter and the Order of the Phoenix, it is Lupin the werewolf who was made prefect. As revealed in that book, each house has one male prefect and one female in each year level, so they couldn't have both been prefects.
Corrected entry: Chapter 6: The Journey from Platform Nine and Three Quarters it says that Harry kept to his room. and Hedwig swooped in and out of the open window. Couple of problems with this: at this stage Harry is still in his cupboard (and it is still called "his cupboard" at the beginning of the chapter, and cupboards don't have windows.
Corrected entry: On page 99, it mentions that Harry and his classmates have Astronomy at midnight on Wednesdays. But on page 173, it says, "Wednesday night found Hermione and Harry sitting alone in the common room, long after everyone else had gone to bed. The clock on the wall chimed midnight when the portrait hole burst open." They should have been in Astronomy at this time.