Its the latter but not the solenoid. Its actually the small switch mechanism inside the gear knob than translates the trigger action to a downward press on ball-bearing over the centre shaft at the top of the main gear shaft to release the lock.A good tip (mine works for months on end then throws a wobbly) is to tap down onto the top of the lever which should release it easy enough.
Not sure if it's a solenoid issue or just "sticky" and needs a grease, but the hardish tap down has always worked for me (I pulled the tab off when opening that centre console tunnel bit).