Key fob locking 2004 Nissan Micra?

My Micra (K12 - 2004 1.2SE) will not always lock on the key fob. Unlock is fine.
It is the same with both fobs & I have renewed the fob battery.

I wonder if Nissan made modifications to the system as my hand book tells me that I can open each door individually from the fob. One press drivers door, Two presses passengers door & so on.
From buying the car the "Open" button operated all doors
On the windscreen there is a box which the rear view mirror is fitted to this has wiring going to it.
Could this be part of the remote locking system? Antenna?
The reason I ask is that the problem started shortly after I replaced the base of the radio aerial & the internal leads are in the vicinity of each other.
If need be how do I remove this cover / mirror? I can find no reference to it.

roger
November 2010