Did you recently replaced the shift knob on the car or something?
I just replaced the shift knob on my car to a better looking after market one and I get the same problem sometime. What I do is I have to unscrew the knob to loosen it up a little bit cause when the shift rod is pressed down, your key wont turn. I tested it like 100 times cause I was adjusting the height of the knob and thats exactly what it is.
there might be something else inside.