I have an automatic transmission and sometimes when I try to put in another gear from "park", it is locked and I have to put the key in the keyhole next to the gearshift to "unlock" it. Any ideas of what may be failing or wrong?

Hey macdaddy181-- Sometimes you put a little to much stress on the transmission and it will lock like that. A good example of a time like that is when you park on an incline and use the transmission to keep the car from rolling instead of the emergency brake. Sometimes you can get out of this annoying jam by wiggling the steering wheel. Other times you have to unlock it like you are doing. If I were you I would remember to use the parking brake more often. That is what it is for. Good luck from Bovan.

Also I've read that it's the solenoid that might be doing it, my car does it sometimes and it hasn't really broken yet, so I usually just pop the key in the shift lock

Other forums say it's a gear position switch problem. Replacing the switch will be the solution.

Check if your brake lights are working. if not then its deff. the braking switch. I just bought a teg with the same prob. replacement switch will cost ya $15-$25 depnding where you go.

most of the time you have to push down on the break peddle to get it in gear-safty feature

What exactly do u mean by unlock it? Im sure u know about depressing the brake pedal. .has the transmission been out of the car recently or did this just start? And theres a spring in your shifter button it could b weak or ill replaced it could b a few things but not expensive ones at least. ..