OK - here's logic for you.

I'd been using the steps across the top of M-Config, rather than clicking on the 800 and store.
It fell over in exactly the same manner - did not receive OK,
Store not successful.
The 800 would then not read disks or works at all - exactly as last time.
Reset the 800 to type 0.

So I have followed the exact path as before.

And guess what!

It now works perfectly.

The pleasures of M-Config.

Thanks for your help Carl!

Enjoy the race!!!

861v8, 2 x 5200SE 5200SEHC, UHD722, Oppo 203EU, Panasonic UB820, PS3.