Intermittent transmission floor shifter will not shift into park

Check the lockout cable for complete actuation. It's the button you have to press to move the shifter. Most likely the cable has stretched or slipped and isn't pulling the lever enough to allow it to move into Park.

there is no cable. if you shut off ignition it will shift into park the reverse lockout solenoid remains out at times.

Okay. Then the solenoid isn't being energized or de-energized correctly. That means the switch that had to be activated to shift into Park is faulty intermittently. And will only get worse.

my shifter likes to stick in park , from time to time.. and now the knob is on the floor.. how can i repair it ?

column or console shift ? knob on floor?

I have a 2007 Buick Lacerne and am having difficulty getting the shifter into park. Soemetimes it works ok, but sometimes it goes all the way up to the park position but will not go all the way left where I am unable to remove the key from the ignition. Is this a common problem with this vehicle? Is it a expensive repair at a GM ealership?

check to see if the clip on thetrans holding the cable has broken. you may need anew cable. otherwise the console has to be removed to check the shifter.