Morning Stephen - I tried sending a message to you, but it said that you were unable to receive messages, so I'm posting the latest news here.
Your thoughts about removing OrbX's Cardiff scenery did the trick. No more scenery fault notice appearing at LFSB. Now I'll try re-installing Cardiff and see if the problem returns. If the problem DOES return, then I'm not sure at this stage what to do about it. To be honest with you, I've been having some reservations with OrBX's addon scenery, particularly their airports. Good as though they are, they do seem to me to be a little inefficient when it comes to performance and my top end PC does struggle a little with frame rates at places like London and KMIA in Florida. Also their depiction of roads is not very believable - they look as if they have been placed as an afterthought and they don't look as if they 'belong' with the rest of their scenery. Anyway, that's by the by. One thing I do know is that this JustFlight LFSB scenery is first class - very impressed tbh.
Just tried starting from Cardiff after re-installing the OrbX scenery - no problems there. So, must have been some sort of corruption in the software somewhere.
Thanks for all your help.