htmlize.el works fine with emacs22 and ntemacs(version 23.0.50)
But when I use the latest emacs-cvs, it doesn't work.
I've cleaned my .emacs, kept only two lines:
(require `htmlize)
(setq debug-on-error t)

Open a new buffer in emacs, then write something in it.
when  "M-x htmlize-buffer", I found these messages:

Debugger entered--Lisp error: (error "Invalid face")
  internal-get-lisp-face-attribute(nil :height nil)
  face-attribute(nil :height)
  htmlize-face-size(default)
  htmlize-face-to-fstruct(default)
  htmlize-make-face-map((default))
  htmlize-buffer-1()
  htmlize-buffer()
  call-interactively(htmlize-buffer t nil)
  execute-extended-command(nil)
  call-interactively(execute-extended-command nil nil)