Help required !!  For Jaguar XJ 6 cireca 2004, The satnav screen has gone blank and the peripheral controls, climate, radio, fan speed etc. are disabled. An error message %0 /51 is displayed.  I am informed that the older software is required to be run to restore the functions.  So far noone appears willing or able to provide a fix. Can anyone help ?

When you have a blank nav screen and a 50 51 on the small green LCD screen this means the screen lost communication with the nav module which is the reader in the trunk. The module will need to be replaced but you can try disconnecting the negative battery terminal cable for about a half hour to see if it will reset.