The error appears to be indicating an intermittent signal from the inhibitor switch, which is mounted on the RH side of the transmission casing. It’s a very common cause of the failsafe message for the 5HP24.

Click image to enlarge

I have exactly the same readout on my delphi diagnostic.

It is the inhibitor/xyz switch whatever you wanna call it. I'm gonna get round to fitting a new one soon. Generally only get the error every now and then when i put it into park. If I get an error when i go to start, i turn the ignition off, then back to position 1 and select neutral and then park. That seems to sort it and allow me to start the engine.

I replaced the same switch on my old p38 as it wouldn't allow me to select neutral at all. Thus stopping me from using the low range box.

New switch should fix it and it's an easy enough job.

You mentioned it's been stood a while. Also worth checking the battery voltage. Not enough gravy in the battery can supply you with all sorts of error messages.

If it's been stood for awhile the contacts inside the 'Park Inhibit' switch (XYZ/PRNDL switch) might have become slightly corroded and become high resistance giving the plausibility error (doesn't know what gear has been selected). I would move the selector a few dozen times to 'clean' the contacts in the switch, reset the error and try again. If the error comes back then probably best just to change it (assuming testing points to the switch being the issue and not wiring elsewhere).
It will eventually go into Trans Failsafe if there is a continuing error and will lock into 3rd or 4th gear when driving which makes pulling out from junctions interesting!

As has also been said make sure the battery is fully charged up as low voltage can pop up a lot of errors especially transmission/HDC Inactive etc.

As RRPhil has also mentioned before on previous occasions so can take no credit for it, if you get the BMW X5 part instead of the Range Rover part the only difference is the cable 'tail' is shorter on the X5 version BUT about £150 cheaper! (on last looking).
If you are handy with splicing cables it could save a nice wedge...something I wish I knew before I did mine a few years back!
The workshop manual is also wrong for the testing of the switch, search for RRPhils excellent posting on here for testing and replacement.

After changing mine I still get an odd error now and again if I shift the lever too quickly.