kizilyildiz as a home user (non-network) I would tear both printers out, reboot, and try again. Solus gives you the IP address, that should help but networking is over my head.
I'm out of my depth here there's a lot of network printer experts on this forum I hope you hear from them.
https://askubuntu.com/questions/994094/i-get-a-cups-server-error-server-error-internal-error-when-i-try-to-connect-a Also-----DDG'd your cups error message and stumbled upon a solved thread:
"'m trying to add a new network printer on ubuntu 16.04 LTS. After setting it's IP address it recognises that a printer is available (192.168.1.100/9100), but when I click Forward I get a CUPS server error: 'server-error-internal-error'. Can anyone help?
The printer is connected to the router and is accessible from another Windows machine." is how it starts