I faced this problem personally and couldnt resist letting you know why it happened!! You must have changed your number plates recently and our dear friends do a very good job when drilling the plates. They drill the number plate on existing lead material and it falls in the locking hatch; inside. Anyways, as already suggested, you can go to Bin Mahmoud and there is only one mechanic who would fix the problem. It is a bit long work coz he needs to open up the entire casing in order to remove that lead material. I think his name is Arvind and his shop is close to the tea shop (i cant remember the name of shop).Source: had same problem couple of months ago;costed me 100 or 150QAR. Good luck!