Peugeot 407: remote fob central locking / alarm problem...

I've an '06 Peugeot 407 and I'm having some issues with some new keys (although I don't think it's the related to the keys themselves!).

The back story is that, a few months ago, my only key was starting to fall apart. I ordered a new case and transferred the blade and PCB. Let's call this Key A. Everything worked fine, although the blade was a little loose. I also bought a second key (let's call it Key which was a blank blade AND a compatible virgin transponder.

After a week or so, I noticed that the range on the fob was getting smaller and smaller until I needed to be right next to the car to use it. I tried changing the fob battery, but it made no difference. Eventually, it stopped working entirely.

At this point, I decided to get Key B cut. That was fine. I have PP2000 and the OBD2 cable, so I coded Key B (and Key A again, per online advice) to the car. All good there too, both keys can start the car, lock it, etc.

I then followed the instructions to reset the fob on both keys (i.e. Insert key, turn ignition on, hold lock button, etc.) but nothing seems to happen.

I tried the BSI reset via opening bonnet, disconnecting battery +, sidelights through the window, etc. as well, but no joy.

With the symptoms mentioned above, it makes me think there's some power source or battery on the alarm RF receiver that's dead. Nothing shows up when I power up the car at all, although I haven't looked too in depth in PP2000 yet. Not really sure what to look for at this point!

Any ideas? Thanks!