Xsara immobiliser

I've somehow triggered the engine immobiliser on a 99 Xsara and I don't know how to get it going again.
The background is that the car belonged to my father who died
recently. I've used it a couple of times without any problems but, on the most recent occasion, the engine wouldn't start and I noticed an illuminated yellow light with a key symbol on the dashboard. I assume this tells me that the engine is immobilised.
Presumably I did something wrong but how do I fix it? I have three keys for the car, two plain and one with a stud which has worn away. I also have a small card which has an alphanumeric code on it which may well be relevant but I don't know how. Unfortunately, the manual is in his home (I assume) and I won't be able to get there for a couple of days.
I got locked in the car as well but the doors apparently unlocked themselves before I suffered too much embarassment. I assume this is related.
Can anyone advise me?
My email address is geod (at) dial dot pipex dot com
You know what to do.
  Click to see the full signature.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.