Rear Reg plate light not working

[Spec]

I've changed the bulb and its still not working. Whats wrong with it? Or.. What could be wrong with it?
The other one (Left) is working but the right isn't

 

[Andy_S3]

Have you tried changing the direction of the bulb? Not sure if this makes a difference but its worth a try

 

[omegadirective]

Not sure if they're on the same fuse, but try checking that?