[Closed] Changing car key cases - no worky

Got a Fiat Bravo - I dropped the original master key down a flight of stairs and the outer case shattered so I got a replacement off Ebay for £25 - removed the innards from replacement and swapped them for the innards of my original key - everything worked - no probs.

Now (through use and wear and tear), the outer fob on this key has broken. I was in the garage and they gave me a replacement key FOC - so again, I removed the innards and put my original innards in the key case. The car locks and unlocks no probs, but when I try to start the engine the immobiliser remains on so the car won't start.

Unsure how this could be happening as the only thing that wasn't swapped over outer shell - that was replaced.

Anyone any ideas? Fiat aren't open yet and last time I spoke to them about keys they offered me a replacement for £130 (that then needed to be prgrammed!)...just wondering if I've managed to forget something or what.

Thanks.