I don't know if it will help. A user had the same problem on 
slackware-8.1 
 
He upgrade first his kde packages and had this problem. 
Removing kdelibs and installing again kdelibs-3.1.1 resolved his 
problem. And now it works CUPS. 
May be a version problem with the kprint_cups.so or something like 
that ? 
 
Have a nice day 
Jean-Christophe Fargette