[exhee]

Easy fix - The system cannot measure adblue quality, it just looks at the resulting emissions after adblue injection and as it does not see the result its looking for defaults to "Adblue quality" message. I suppose if you put water in the tank or something then its working on that basis. Any aftermarket Adblue you buy in the shops is perfectly acceptable, it meets standards.
The problem almost certainly is the adblue injector has gummed up, and its mating port on the exhaust. You can remove and clean it, clear down the fault code with most code readers (no need for Jaguar/Landrover dealer) and it will change message to Dosing Fault. After 10 to 30 miles the warning lights just extinguish. If the fault reappears (or if you are so inclined) then you can change the adblue injector for a new one (part number is FX23-189E3-AA). The whole job cleaning or changing takes just 30 minutes and only tool you need is a 6mm allen key (oh, and a jack). See this video for brief explanation of how to do the job but there are a number of examples on Youtube to get a complete perspective.