Problem resetting Adblue warning

[cd1957]

Hi all,I have a customer with 2016 Cayenne.
The Adblue warning came on saying,Car will no longer start in 250 miles.
Customer topped up level as he has done n the past.
The light went out, but came on a week later.
Tried to reset with PIWIS 2, no change.

Anybody come across this before.

Chris