Not sure what solutions have come up in this thread (too lazy to read it all
), but this happens to me once in awhile, and I found that all that is needed - for automatics, anyway - is to press the shifter button a few times while in park - after a few presses you'll hear a click in the steering column which is the solenoid holding in the key or something, so either the solenoid is sticking/faulty, or it just isn't getting the command to release/energize (i.e. problem with the shifter).
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