Colleagues,

Thank you all for your help with this problem. I tried all your
suggestions, including checking the 'hosts' file and creating a completely
new Location.

Nothing has worked. It is just so completely weird.

Anyway, the owner is going to call out a proper Apple technician to sort it
out. If the owner is able to follow what the technician does I'll report
back, just for the record in case somebody else suffers this problem.

Meanwhile, thank you again for trying to help. Really appreciate it.

SteveT