cups/printer seem to have crashed

I have used my printer (a Laserjet 5p) without any problems for a long while when suddenly it stopped printing (from any application). I tried re-running the printer configuration utility of KDE, but when I try printing a test page I get the error "unable to create temporary printer" and when I ignore it and try to create the printer I get "client error bad request". As a user, which is how I used to print I am member of the following groups: username dialout fax voice cdrom floppy tape sudo audio dip video plugdev games users usb scanner camera fuse. "Lp" is not among them. I tried doing "sudo adduser username lp" (substituting my real username of course) which added me (as a user) to lp. However, when I type "groups" then "lp" does not appear in the list. When I do sudo adduser username lp again it says that I am already member of this group.

I know that this is not a hardware problem as I put a Kanotix live-CD into a drive and when through exactly the same configuration steps and my printer worked perfectly (test page printing and all).

My feeling is that some installed application has done damage to my cups server or/and to my groups.

Any ideas as to what I should do?

Many thanks,

VS