Thanks for that. David, I tried your suggestion but nothing will make the test connection work. I even switched off my firewall and made the PC share visible to the internet - eek! But I needed to rule out everything. So by the way StephanB, yes, the share is very visible. I can usually acccess it from my laptop over the home wifi.
On thing - David mentions 'server'name. My PC isn't a server, it's just an ordinary household PC. Does that make a difference?
Going back to David's suggestion, using the following prefixes:
and no prefix
I have tried adding every type of name to the Host: field, including:
192.168.0.2 (my IP for that machine, obviously!)
Hard-Disk (the drive name on the PC)
$c (I got that from another part of the forum discussing this issue)
c (the usual hard disk designation)
c: (as above)
GABRIEL (the PC's name - at one time I had 4 computers each named after an archangel. I'm not religious but it amused me to name my wireless network 'Seraphim').
Nothing works. Of course following David's experience, it might be the case that one of these non working configurations might produce a working backup, but life's too short, and with none of them producing a single instance of a successful test connection it's completely discouraging. If there are any other configurations / names / aliases / runes you can think of that I might try, feel free to suggest. Thanks for trying guys.