Help with central locking!

[LeadFoot81]

Hey guys and girls, my central locking (Au2) is refusing to lock all four doors (with remote or key) the interior lights stay on even though all four doors are properly shut.

I had a drama early last year where my back right door wouldn't lock, but it seemed to sort itself out. The same door suffered from a very stiff exterior handle didn't work for a while, this also sorted itself out. The same back door is now the only one that will lock!

Sjrn the problem started I thought it's the actuator in the back right; but now I'm lost. If anyone with experience can put me on the right track I'd appreciate it!