Replaced immobiliser on 96/97 EK civic sedan

I managed to do the worst thing possible by misplacing the transponder chip in my only key (the rubber sheath wore and chip fell out) on my civic. Since I don't have a red key, I was quoted $900 by honda to replace the whole immobiliser system. Naturally, I told them to shove it where the sun don't shine and made way straight to the wreckers.

Picked up a second hand immobiliser, ecu and key set. Had that put into the car, but the auto mechanic still can't get it started! The green light still turns on even with the new immobiliser, ecu and key.

Any idea what is wrong, and what can be done to resolve this?

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