[O] Error when running publishing Org example :(void-variable org-publish-attachment)

[Matthew Kenworthy]

Hello all,

I'm running the example for publishing an org site to html at:

https://orgmode.org/worg/org-tutorials/org-publish-html-tutorial.html

...but when I try to execute the "org-static" block, I get the error:

(void-variable org-publish-attachment)

...any ideas as to what I'm missing here?

Many thanks,

Matt