Problem with Luxi mono font.
if you have debian SID (but also if you don't), could you please make
the following test?
apt-get install ttf-xfree86-nonfree
And see if KDE recognizes Luxi Mono.
Kde-control-panel -> Appearance&themes -> fonts -> fixed-width
Does the font appear in the list? On my system (SID), it doesn't (bug).
Does it appear in the general list?
Kde-control-panel -> Appearance&themes -> fonts -> general
on my system (SID), it does (no bug).
If (1) does work, please also disable the bytecode interpreter in
then reboot kde. See if it works again.
Now please tell me which distro you are using: sid, sarge, woody.