Raspberry Pi + CUPS = no web interface login. Help, please?

Hello reddit!

I want to set my Raspberry Pi up as a printer server for my local network. It's running Raspbian.

So I installed the required packages

apt-get install cups printer-driver-gutenprint 

And then set up the remote access for the web interface and printer sharing.

cupsctl --remote-admin cupsctl --share-printers cupsctl --remote-printers 

In the end, I added my user account to lpadmin using

usermod -aG lpadmin pi 

Now I enter the IP address of the pi and the port for CUPS into my browser window and can access the web interface. However, I am stuck at the login window when I try to add a printer to the server. It asks me to enter my user account login and password or root login and password and neither of those two works. Can anyone give me a hint as to what the problem might be?

Thanks!

Phil