Is is an automatic?, make sure it is engaged full into the Park position. I know this sounds stupid, because you have probably done that a few thousand times. But if you are in a hurry and panic, you may not recognize you did this.
Try moving the steering wheel back and forth (gently) as you try to take the key out of the ignition. This sometimes will work.
The nuetral safety switch may have gone bad. I hope this helps. Trying to diagnose this on the computer is frustrating for both of us, I would bet.