I have connected a USB thermal receipt printer to a laptop running the latest version of Debian. I then tested the connection to this printer by logging in as root and issuing the following command "echo "Test" > /dev/usb/lp0" and the word "Test" printed successfully.
I then opened a browser and typed "localhost:631" and found CUPS 1.7.5 was installed by default. The thermal printer came with a Linux driver so I installed through the CUPS web interface but it seems I have a problem.
When I attempt to print anything to this printer, it does not print out the actual print job but instead a message saying this script requires root user access. I have this same message whether I am printing from an application such as gedit or trying to print a test page through the CUPS web interface.
Pretty sure it's a permissions issue but what confuses me is that I accessed the CUPS interface to add the printer under a standard (non root) user. Therefore as I added this printer with a standard use account, I can't understand why I can't print to it?
I don't have a debian system to check your issue. But you may look inside /var/log/cups/error_log file to see the errors relevant to your case. Also you may check /etc/cups/cupsd.conf file for configuration issues.