Errors in Harry Potter series

Though I agree that HP is a very good book & movie series,there are quite a few errors in it.

• James Potter had also given his life to protect Lily & Harry, so they should have got his protection. Then how come Voldemort was able to kill Lily ?
• The Elder Wand is undefeatable in any duel. So how could Dumbeldore defeat Grindelwald (the owner of the Elder wand) ?


• You can't apparate or dissapparate inside or outside the Hogwarts grounds. So in the 5th book, how could Marcus Flint have apparated from the Vanishing Cabinet into a bathroom? In the 6th book Draco Malfoy says - "In the end, he succeeded in apparating outside the cabinet, even though he hadn't passed his test." How ?
• In the 1st book, Hagrid says, "Hogwarts is the safest place." Even though the staff had applied their best efforts to guard the Philosopher's stone, three first-years were able to break through the defenses. Also, only a simple lock was put on the door of the corridor. It was easily opened by a simple Alohomora spell.What kind of protection is that ?
• In the last book, when Nagini corners Harry at Godric's Hollow & summons her master, why couldn't Voldemort have apparated directly to that place? Why did he have to fly? Same is the case when Bellatrix summons Voldemort to Malfoy Manor?
• Fred Weasley dies on 2nd May, 1998. In one of her interviews, J.K. Rowling has incorrectly stated that he dies in 1997.
• According to James & Lily's tombstone in the the last book, they died on 31st October, 1981. That means Harry was taken to the Dursley's on 1st November. In the 1st book, that day is described as  "the dull, grey Tuesday our story begins." But if we check the calendar, 1st November was not a Tuesday; it was actually a Sunday.