Message goes "There was a problem during the CUPS operation: 'client-error-not-possible'."
I follow a protocol that I used on Ubuntu 16 many times, but now I reinstalled to Ubuntu 18. I start from running the command "system-config-printer" from a terminal window.
Click on "Add printer" --> "Network printer" --> "Windows printer via SAMBA". Then tick "Set authentication details now". I provide my name and password. - Click on "Forward". Then you will see a message about "Searching for drivers", wait until a dialog box is shown. Choose "Provide ppd", browse to the ppd -file that I fetch from a local list.