On 18.04, I have just had success with the following:
On Ubuntu:
Install smbclient and add client max protocol = NT1 to /etc/samba/smb.conf as per L.D. James' answer (see this post for more info).
On Windows: Create a folder in Windows to share, e.g. named shared.
Make sure the folder is shared: I created a new user on Windows, keeping the NewUser name and selected a simple password (I first tried changing the name, but found that change was apparently only skin deep. Perhaps if I had rebooted...). I logged in with NewUser, then logged back in with my admin account. I activated network sharing on my private network and for the folder specifically (see e.g. this post). Then I right clicked the folder and chose Give access to..., choosing NewUser (you may want additional permissions: see the just linked to post). Under the Sharing tab, the folder now has a network path: //COMPUTERNAME/shared.
Still on Windows:
To gain access to the shared folder, I used the IP of the Windows machine instead of the COMPUTERNAME, cf. this.
To find the IP of your Windows machine, right click the network logo, open Network and Sharing Settings and choose Change connection properties. Take note of the IPv4 near the bottom.
In Ubuntu:
Finally, open a terminal on you Ubuntu machine and execute
sudo mount -t cifs -o username=NewUser //[insert IPv4 here]/shared /home/your_ubuntu_username/shared
and provide the password for NewUser when prompted.
This mounts the shared Windows shared folder as a folder shared in your Ubuntu user's home directory.
The command is based on suggestions from here, where there are also suggestions for storing login credentials.
I hope it works. Good luck!