Parking Brake release
 

I have a 2011 Lucerne CXL with approx. 99K km on it. For the past six months or so my parking brake has been giving me trouble. Half the time it works well however sometimes it will not apply. The pedal will not push down at all. It's like hitting something solid - like metal on metal. If I drive it a few km it will work fine again. When it does work - it always disengages OK (so far).
Any ideas? Thanks