Slackware 13.1 uses Ruby 1.9, and this could be the cause of the problem (IIRC there were reported issues between Ruby 1.9 and KDE 3.5.10).
Yes, I remember the discussions. The recommended fix was to create two sym links. My build scripts create them but I verified both do in fact exist. Further, Amarok needs the same links and that package built without error.
Darrell