"Unknown" error when modifying or adding printers in RHEL 6.9

Issue

• When we use cupsenable or cupsdisable we get the following error

  cupsenable: Operation failed: server-error-service-unavailable
  

• Issuing the following command:

  # lpadmin -p HPP2 -v 'socket://10.1.4.2' -E
  lpadmin: Unknown
  

• An attempt to set printer default options when using the CUPS server web interface results in an "Unknown" error. This behavior did not occur until these three RPMs were installed: cups-1.4.2-77.el6.x86_64, cups-libs-1.4.2-77.el6.x86_64, and cups-libs-1.4.2-77.el6.i686.

• Running the following command doesn't work properly in RHEL 6.9. As you can see, the device isn't set properly:

  # lpadmin -p printer -E -v lpd://192.168.121.95 -m raw
  lpadmin: Unknown
  # lpstat -v
  device for printer: ///dev/null
  

• When "Requires user @SYSTEM" or "AuthType Default" was used in the tag, the cupsenable, cupsaccept, cupsdisable, lpadmin, and possibly other lp* commands could terminate unexpectedly.

• When using the cups-lpd service to accept print jobs from remote Unix clients, we are seeing the following error in /var/log/messages:

  May 11 14:01:41 dehb-pserv-21 cups-lpd[24249]: Unable to create job - Unknown