Mine had the same issue. Put the new coil in and the problem was solved.
http://www.pinwiki.com/wiki/index.php?title=World_Poker_Tour

I had this issue. Bars stuck up. The mech is easier to work on than people say. Yah, it's kinda a pain in the ass because it's in the back, but it's just 6 screws and some connectors.

Anyway, when I removed the mech there was a bunch of dried up gunk (from the factory I'm sure) that just made everything sticky.

I took it apart (just some e-rings basically) cleaned it all up, used a light oil based lube, put it back together and it's 100%.

That might be your issue, but don't worry about working on it. Should be easy to tell, if the bars are up and not dropping, try and pull them down by hand. If they move, it's probably just gunky.

I have this problem as well sometimes when I've been playing for a while. I think I'm going to try swapping out the coil. Which of these two is the correct one?

http://www.marcospecialties.com/pinball-parts/090-5072-05

or

http://www.marcospecialties.com/pinball-parts/500-6976-01

Did you test the rear opto? I would put it in switch test. An op friend of mine has one and it had the same problem. It turned out the rear opto was bad. I replaced it for it and it works 100%. Don't replace the coil if it resets when you turn the machine on. The Opto boards are pretty easy to repair if you have basic troubleshooting skills.

In my case, both sets of optos appear to be functioning like they should. The game will work perfectly when I first turn it on, but after a while the bars will stop dropping consistently. Even at this point, the optos still test fine.

The spring that pushes the jail bars down can weaken. Mine did recently. Because the game was on location and I didn't want to wait for parts, I stretched the spring slightly and that fixed it. Don't recall how it acted in test.

Just put your finger in there. You don't need to use a ball. Put it in switch edge test. There are two optos, I can't recall the switch number but one is called Jailbar Bash the other is Jailbar Rest. The jailbar rest is the one you want to make sure is working.

Good news. Thanks for the follow up.

Where'd you find the board for $32?

Holy shit! !!! $18 to ship?

So I was going to replace the rear opto in my WPT last night. I noticed the upper PF looked a little cloudy. I novus'd where the rear opto is and voila it works perfect now. You might want to try that in the mean time.

I had the same issue with the jail bars not coming down, My fix was to upgrade to software version 14, remove the small coil and unwind 225 winds (started with 100) to make the coil stronger and cut 2 rounds off the coil spring and it works like a charm. Coil resistance was 14 ohm to start and 8 after removing the 225 winds. I ordered a new coil and spring as well, but got it fixed without having to wait for parts, which is always a plus. Hope this helps someone