screw won't come out!! :(

[hedpe]

Hey all, I'm having extreme difficultly (in a W126), and I mean extreme, of getting a screw out. The track that the passenger seat is on, not the silver track, but if you lift up that brown cover there is a black track. I unscrewed the factory screw and put a longer screw in, and now it won't come out! I've tried prying it out with all of my force, hammering at it to strip the screw and pull it out, but it seems that you can push on it, and it pushes in, like its caught on some sort of device that's meant to keep it in there. Anyone know how i can get this thing out? I've spent over 2 hours trying to pry and unscrew and get it out. I'd really appreciate it. Thanks!