I also looked at other systems with Oneiric installed.
a) an upgrade from Natty - works correctly
b) a new Oneiric install - works correctly
I found that my problem was caused by an entry in /etc/cups/printers.conf for a printer that no longer exists.
The entry was for the <DefaultPrinter> section.
I fixed it by these steps:
Stop CUPS, so we can edit the conf file safely
> /etc/init.d/cups stop
I also looked at other systems with Oneiric installed.
a) an upgrade from Natty - works correctly
b) a new Oneiric install - works correctly
I found that my problem was caused by an entry in /etc/cups/ printers. conf for a printer that no longer exists.
The entry was for the <DefaultPrinter> section.
I fixed it by these steps:
Stop CUPS, so we can edit the conf file safely
> /etc/init.d/cups stop
Edit /etc/cups/ printers. conf
from:
> <DefaultPrinter>
> ...the non-existent printer entries...
> </Printer>
> <Printer>
> ...a valid printers entries...
> </Printer>
to:
> <DefaultPrinter>
> ...a valid printers entries...
> </Printer>
Restart CUPS
> /etc/init.d/cups start
I can only assume that system- config- printer- kde needs better error handling.