gnus registry menu problem in emacs 23.1

[Paul Bibbings]

To give the context, I recently upgraded to Emacs 23.1 running on
Windows Vista, and followed the instructions in `gnus-registry.el',
adding the lines:

    (setq gnus-registry-max-entries 2500
          gnus-registry-use-long-group-names t)

    (gnus-registry-initialize)

to my ~/.gnus.el file.

In ~./.emacs I already have:

    (custom-set-variables
       ...
       '(gnus-registry-install t)
       '(gnus-registry-marks (quote (
            (Important :char 105 :image "summary_important") 
            (Work :char 119 :image "summary_work") 
            (Personal :char 112 :image "summary_personal") 
            (To-Do :char 116 :image "summary_todo") 
            (Later :char 108 :image "summary_later"))))
       '(gnus-registry-max-entries nil)
       '(gnus-registry-use-long-group-names t)
       ...)

If I then check everything after loading gnus:

   1. `C-H f' gnus-registry-set-article-Important-mark (for example)
       tells me this function is available in `.gnus.el'
   2.  With an appropriate article selected,
           `M-x' gnus-registry-set-article-Important-mark
       executes as expected and sets the mark.

However, with the same article selected as in 2. (above) clicking on the
menu item:
     Gnus | Registry Mark | Important
fails with:
     "Symbol's function definition is void: 
         gnus-registry-set-article-Important-mark"

Is anybody able to help me understand what the problem might be here?
I'm at a loss, being quite new to Emacs and Gnus (though loving it, I
have to say). The menu item seems to be hooked into the correct function
call, but it is somehow believing that it is undefined, whereas the
other tests (above) show that it clearly is, and operates properly.

Thanks in advance.

Regards

Paul Bibbings