I suppose you are using the contributed Slackware packages from KDE website? I had similar problems with them. There seems to be some symbolic links missing, so to correct things you have to type (as root):
[code:1]cd /usr/lib
ln -s libaudiofile.so.0.0.2 libaudiofile.so.0
ln -s libvorbisfile.so.3.0.0 libvorbisfile.so.0
ln -s libvorbisenc.so.2.0.0 libvorbisenc.so.0
ldconfig[/code:1]
That's what I had to do, your installation may throw up some other similar errors, so adjust accordingly.
I think there is something strange in those Slackware packages :?
JR