I chose to upgrade our Confluence installation that was running 4.2 to 4.2.4, due to some stability and plugin install issues we were experiencing. The upgrade went smoothly, but I just found that some embedded HTML content was no longer working, what was appearing was an error in the page:
Unknown macro 'html'
The HTML include macro was also not showing up in the macro browser.
The solution? Re-enabling some modules for the "Confluence HTML Macros" plugin. Instructions for re-enabling the plugin are found on Atlassian's site here.
I enabled to modules:
and things were up and running again after that. It seems confluence may have added this xhtml module since the 4.2 release, and caused a conflict which lead to the modules being disabled.