Yesterday I left the xjs-v12 outside and was able to lock it with the fob. In the morning, it opened fine.
Later it locked and stayed locked.
On unlock, it went into alarm state by chirping (low) several times - hitting the button turns it off.
The key opens all the doors.
Changed the A23 battery on the fob - same reaction. Tried second fob, same reaction.
Is something on or open, or what?
It’s presumably a 6.0 model? 
Take a look at the condition of your vehicle battery to make sure that it is up to a full charge - Tex.
v12 1994 6 - that’s right
the battery is fully charged on a trickle charger - and starts up just fine every time
after being outside for 12h - the check engine light lit but then went off on warm up
Make sure both doors and trunk are fully closed and latched.
The interior latches can come loose and may need to be re-positioned and tightened.
I sometimes had a problem when the door didn’t quite close all the way.
After checking these things you might want to invest in a new security ECU.
A NEW SECURITY EDU ? The battery is fairly new. The doors and boot all close fully.
In addition to the fob not working - the key will not lock the doors or the boot, and the inside door locks will not lock all the doors (previously the driver’s latch will lock both doors). Surely this is a common cause - any help is appreciated. Thank you.