Printer Proxy permission problem.
In response to other queries regarding lack of printer proxy permission when trying to print. I have parental controls set on and thought the problem was linked to that, but nothing I tried seemed to cure the problem. The fix appears to be : Enter system settings and choose network. Once in network unlock with admin password and choose advanced button. Go to Proxies tab and tick the Auto Proxy Discovery box (and the 'Use Passive FTP Mode (PASV) box at the bottom). Choose save when exiting system. If this doesn't fix the problem, go back to proxies in advanced settings and also select Automatic Proxy Configuration, specifying the URL for an automatic proxy configuration (see administrator for this).
iMac 21.5", macOS 10.12