Hello Richard S and Welcome to Wolvix.
I found that I have the same problem as you describe above, I did manage to resolve the issue though. Here's what to do until I create a new package to fix the issue.
Stop CUPS, then do this (as root):
cd /usr/share
rm -r doc
ln -sf /usr/doc doc
Then start CUPS and try setting up the printer again.
The problem is that CUPS has been compiled to use /usr/share/doc as it's document path. Slackware's default doc path is /usr/doc, so it has a symlink from /usr/share/doc to /usr/doc. This symlink has been broken and replaced with a directory in the Wolvix modules it seems.
I'll try to work out a solution for the issue, but give the above a try.