I've never had this issue since owning my XKR. The past few days whenever I get out of the vehicle after its turned off with either the fob in my hand or pocket I press the black lock button on the door as I usually do and I keep the double error beep as if the fob is left inside the car. I press the lock/arm alarm button on remote and nothing happens as it does not lock or arm the alarm. Sometimes if I give it approx 10 plus seconds or so the fob will work and all is well. It seems to be intermittent with it working sometimes and others times not working. All the other buttons seems to work fine and I never have any issue getting into the car. I changed out the fob battery today and it seems the same thing is still occurring. I installed a new car battery only 6 months ago so I know its not that. I even placed the fob more than 3 feet away and hit the black lock door button but still get the error beep. Anyone that has any advice or had this issue before please share as its quite annoying to me to go somewhere, get out of the car and just stand there for a while trying to lock and arm it. Thanks guys.

 

Try disconnecting the negative terminal on the battery for 10 seconds or so and then reconnect it. This should reset the system.

Also, while you are at the battery, check the voltage with the engine off after the car has been off overnight. Occasionally new batteries fail. A good battery should be over 12.4v or so. Some battery failures can still provide plenty of current to start, but not enough voltage to maintain the electronics properly.

 

You probably have a 'mislock'.
From the X150 Workshop Manual:
>>
If any doors, liftgate or hood is open when a lock or double lock request is received, the anti-theft alarm system remains disarmed and the CJB generates a short mislock sound on the vehicle horns, battery backed sounder or passive anti-theft horn and the turn signal indicators will not flash.
Each attempt to lock will be confirmed by two audible chimes being emitted.
<<
I get this if a door or the trunk is not closed *firmly* - the microswitch thinks it's still open.
Two suggestions:
1. Charge the battery on a trickle-charger until the charging current falls to zero. Its possible your nearly-new battery is discharged by short journeys etc
2. The next time this happens, open and firmly close each door etc in turn, trying to relock the car each time. If it starts working, that door needs adjusting probably.

If that fails, its possible there's a error code logged. A dealer. or *sophisticated* OBD reader can retrieve it (it won't be a common error code - probably Jag specific).

Good Luck !