Fire stick – “This app is not associated with your Amazon account”

HI All,

Im having a problem and i wondered if you can help.

I installed Kodi 17 + a full build, on a couple of fire sticks and they were working fine on Sunday.
I took them round to my mothers house yesterday and proceeded to show her how to use it.
When trying to open Kodi, It launches the Kodi Krypton 17.1 page and then the screen goes black and goes back to the Amazon Firestick apps page and say “This app is not associated with your Amazon account” under the description of the Kodi App.

What have i done wrong? it was definitely working on Sunday!

I have tried the following:-

Force Stop
Clear Cache
Clear Data
Changed Virgin Internet Settings to allow all websites
Tried to delete reinstall
Reset back to factory Settings and reinstall (Allows me to reinstall but not open)

Please help! Any suggestion of how to get it working again? Or even why it is happening?

Thanks you in advance!