I have a C5 on a '51' plate and have a similar but intermitent problem.... Rather than the boot open alarm been constantly on I get a message on the lcd display saying the Right Front Door is open, even when it is securely closed. I then get the identical problems when I try to lock the car with the remote fob with getting the 2 clicks of locking then unlockin... or with the key I can lock the front doors but not the boot or the rear doors... which cannot even be locked manually from inside the car.
