I just updated to Lubuntu 15.04 and now I cannot print to my HP Wifi printer. The printer shows up as a wifi network but I cannot connect to it. It keeps asking for a password when the printer is not password protected. The printer doesn't show up under system-Tools --> printer either. All was working fine before the update.
in my case, if printer is not shared, it does not show up in system-Tools --> printer
i filled this report
it's still a mess for me, hope it helps you a little.