Midnight Commander's SMB implementation uses a very old version of the CIFS protocol which Samba disables by default.
You could fix it by adding:
server min protocol = CORE
client min protocol = CORE
to the [global] section of the /etc/samba/smb.conf file.
This makes Samba enable a very insecure version of the CIFS protocol which you should never use unless you have your own private LAN with only trusted devices.
A pertinent bug report: https://midnight-commander.org/ticket/1