The bolt threads in like any standard bolt... Crank arm is threaded.

I don't remember anything special to remove it. I'm using Stronglight rings on my cranks, and think I'm using all generic chainring bolts (the Stronglite 34T ring has 4 threaded holes + 1 unthreaded).

I did lose that 5th bolt once, and now am using Purple Loctite on it, so perhaps your bolt is just stuck a little bit.