There are a few glaring ones... When Harry wanted to become an auror in the 6th part he was told that no new witches/wizards were recruited in the auror department in the last 3 years, whereas in the previous book we found Tonks to have recently joined the department as an apprentice under Moody.
Harry was afraid to join Slytherin because he was told that's horrible... Had someone explained to him properly like he did to his son, he wouldn't have felt that scared.
