When I tried to connect to the administrative file share C$ on my wife’s computer I got the error A device attached to the system is not functioning.
The other way round worked without a hitch, i.e. I could access my laptop’s C$ share from my wife’s computer.
When I tried to connect to her computer on the commandline I got this:
d:\>net use \\Computername\C$ /user:Computername\Username * Type the password for \\Computername\C$: System error 58 has occurred. The specified server cannot perform the requested operation.
Different error message, same result.
After fruitlessly poking around some more I finally had the idea to check the target computer’s firewall settings. And indeed, file and printer sharing was disabled:
After enabling file and printer sharing for private networks and also disabling UAC remote restrictions (we are in a workgroup environment, not in a domain) things worked as expected.