I found out that the information in the tutorial is ambiguous and I could only make it work on a HEAD installation. Well, I could at least make this one work:
https://openacs.org/doc/openacs-5-1/ch10s06.htmlThere are actually two documents about categories in the tutorial: https://openacs.org/doc/openacs-5-1/acs-package-dev.html
Hope this helps.