[Warning Light] Immobiliser

[Lwt Big Cheese]

I hate to be a newbie on here and start with a question! Anyway...

I have just had my 'proper' car written off, so I had the opportunity to buy a 2000 Berlingo and took it! It has been stood for a while, so I changed the dead battery and then jet washed off all the green algae. Started her several times yesterday.

Got insurance sorted today and then went to start the car. Nothing. Well it turns over OK. Noticed the Electronic Key Not Recognised warning light lit up.

I only have one key. It looks just like an old fashioned key. Why wouldn't it be recognised now?

Any ideas chaps?

TIA