Both keys unlock, only one will start the car
 

I have a 2007 VW Rabbit(US Golf).
I was given two keys with the car and until recently only ever used the one. Was in a rush so I grabbed the spare and was able use the clicker to unlock the doors.
When I put the key in the ignition it started the car for a few seconds then the engine died.
On the instrament panel shows a car with a key inside it which i can only image is an anti theft ignition kill indication.
Went in the house and grabbed the other key which started the car without issue.

Do I need to 'program' the key?
Is it something I can do myself or should I contact the dealer?

Thanks for any help.