Number plate lights

MOT fail I meant! This was a new Audi part too, but clearly either something is wrong with my wiring - or the car does some sort of 'different' check on its systems at certain times? Otherwise I cannot work out logically how the problem can reoccur randomly.
 
I will get my bulbs from Audi then it looks like as those units of an A8 ain't a bad price. I have bi xenons and drl is activated in mind but the bulbs in the headlight are the normal yellow ones , is it pissible to change these to LED ? As I assume to get the real drl look into the headlight would be mega bucks ?

Si