Who de-activated ground-air missiles on 9-11?

The Pentagon is protected by a computerized system. When a plane
enters the pentagon protected space the computer automatically sends a
message to the plane demanding the pilot punch in a code allowing it
to enter the space. If that is not done within seconds, the plane is
automatically shot down with missiles

Now you might say the hijackers knew about this and demanded the pilot
of Flight 77 give them the code. But surely he would have given them
the wrong code and there would be no time to retrun to the pilot and
beat the correct code out of him.

Either the missile system was de-activated that day or someone gave
the hijackers the code before-hand.