Cups error - "An error occurred while retrieving the printer list. ": why ?

[Mark Ryden]

Hello,
I have a machine with newly installed  Fedora Core 6 (i386).
I had ran "yum update" on that machine.

When starting kprinter I get the following error message:

An error occurred while retrieving the printer list.

Connection to CUPS server failed.
Check that the CUPS server is correctly installed and running.
Error: the IPP request failed for an unknown reason.

service cups restart does not change anything.
rpm -q cups
cups-1.2.7-1.3.fc6

There is NO firewall running on that machine.

I also ran "tail -f /var/log/cups/error_log" when starting kprinter,
yet I don't see any message in that log when kprinter is starting.

It is a fresh installation of Fedora Core 6. I did NOT yet installed
printers using cups/kprinter on that machine.

I can enter the web interface from a firefox browser by:
  http://127.0.0.1:631 without any erros or problems.
	
Any idea what can cause this error message?

Regards,
Mark