sounds like you hit the key.
Were you trying to heel and toe while slowing down?
It happened to me in the same situation.

 

If the green immobilizer 'key' blinked at you, your ignition switch got turned from the 'run' position to the 'accessory' position. No ands, ifs, or buts about it.

You turned the key with something.

 

Or....there's an electrical problem in the ignition, and the car 'thought' the key moved to the ACC position momentarily. I'd have Honda check it out, they just may find something wrong....

 

If you were moving your leg from gas to brake, that's when it seems most likely to happen, which it sounds like what you were doing. If you have your remote or other keys attached to your keychain they could have just been at the right angle that your knee touched the remote and that in turn turned the key....it's happened to me before.

 

you took your foot off the clutch pedal? I really hope this isn't what happened because it would be a sad day for the s2000 community. Or cars in general

 

This is new to me. I've driven my car hard for up to 10hrs straight many times, never had it shut down on me. Nor am I aware anyone who has.

Is this really normal?

 

Heat soak can happen, but the length of time really doesn't matter.
Try driving your car super hard for a couple of hours.
Ex: In 2~3rd gear and vtec the whole time.

I've experienced heat soak once and the car would bog down in the lower revs while tring to take off.

 

Heat soak or not having the clutch in would not cause the immobilizer light to come on and the instruments to go dark.

I'm with the key theory but you may not have hit the actual key with your knee, you may have hit the key chain with your knee (if you have one that dangles).

 

I think my knee hitting the key chain is more likely cause I've been driving my car the whole day and it runs fine........at that time I didn't let go the clutch, I didnt have to step on the clutch either cause I was slowly decelerating from 5000rpm-------------> 4000rpm in 2nd gear where all of the sudden my intrument lights just went all dark and the immobilizer green light came on.....So I think I did hit the key or key chain somehow when I was hitting the brake.........But thanks for the help guys.