I did eventually succeed
1) Ensure the homegroup provider service is running. See if homegroup can now be left
2) Turn off all other computers than the one you are currently working on
3) Try to delete the files in the folder I mentioned above
This will ensure no homegroup - old ones even to which yyou don't know the password - exists
4) Before then creating new homegroup bear in mind that ideally both/all computers should connect to the internet (temporarily) the same way
MY desktop has a wireless card so I could use that to connect to the router
(Due to complications in my house I have a wireless extender and a mains network connection thingy - don't ask)
5) I created the homegroup on my wife's laptop, then leaving it on, powered up the desktop, joined the homegroup with the password given on the laptop
Just to share a printer!

No guarantees but this worked for me