show-wspace.el fontlock problem

[Neal Becker]

I'm trying out show-wspace.el:

http://www.emacswiki.org/cgi-bin/wiki/show-wspace.el

Sort of works, but I'm getting millions of messages:
Fontifying region...(invalid-function 0)

Strangely, setting debug-on-error doesn't seem to trap the message.

I'm thinking this should be simple to debug.  At the end of show-wspace.el
there are several font-lock-add-keywords that I was thinking might be the
cause, but I don't see it (I'm just going from the font-lock-add-keywords
doc, I don't have any experience with this).