The shifter in my Jeep Liberty get stuck and will

simple
look at rear of car, brake lamps out
bingo!@@ dead !
the brake lamp switch must work or the parklockout feature (by law) rears its ugly head.
1000s of posts here, same subject, you will not be first.

park lock out
its feature and the law in USA< are you.?

the break lamps most work
and for SURE the brake lamp switch.
1000's of posts on this topic, and all the same, due to laws mandating it.

posible problem whit sifter interlock selenoid or circuit

WD-40

The first thing to do is check the brake lights, it they are not working the park lock system will not release the shifter.

This is not intended to sound rude, but have tried depressing the brake as you attemp to shift? I am the guy that all my friends call for advice and believe me this would not be the first or the last time for this question in my lifetime.

Rock back and forth , take it out of AWD , Put parking brake on shift into Park .

Well, Im not sure on your specific make, but I can't believe Jeep is still having this problem, My 2000 Grand Cherokee was always doing that. Usually, (It was the 'ol hammer trick,) in at least keep jamming forward on the (floor stick in my case) shifter and keep trying to start it. ( while it's in Park, but just kept hitting it forward) Best I got, there was just that glitch, but always worked whenever it may have happened.

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refer to
http://askville.amazon.com/2006-Jeep-Liberty-Sport-stuck-park/AnswerViewer.do?requestId=3458924
discussion here,
http://askville.amazon.com/2006-Jeep-Liberty-Sport-stuck-park/DiscussionBoard.do?requestId=3458924&page=1