Thanks,
I started with NovaStor forum but got viewers only, no reply.
The program had worked perfectly on my drive P (a partition on the hard-drive in my laptop) for half a year.
Now I renamed a few folders, so it'd got the 'right' to stop, but then I used the same installer as earlier.
The full error message is this:
Failed to find node:
/configuration/appSettings/add[@key='DefaultSubscriptionGroup']/@value in XML file:
C:\ProgramData\NovaStor\NovaStor
NovaBACKUP\Profiles\ManagementServer.Agent.Service.exe.config,
system error: -2147020584