I have update the plugin to version 0.23 and fixed a few problems:

• The keyword cache file is now rebuilt from scratch rather than waiting until all the stories have been viewed.
• Rebuilding the cache can be forced by appending ?refresh=full to the url.
• Bug fixed which stopped stories being viewed if they were in the blosxom main directory (ie not in a category) when /keyword was being used.

Download the latest version (version 0.23).
Further instructions are in the zip file.
There are still some problems with using /keyword instead of ?keyword= but they don't seem to be critical.