JOOMItaly - Professional Joomla! Extensions

The latest thing to do is to ask to your server administrators to let them works properly. It's almost surely a permission problem (not necessarily a chmod problem...)

Thanks to my friendly site administrator I got the advice that allowed me to resolve this problem.

In a shockingly unhelpful approach I was advised to look at the site logs for the HTTP 500 error that was occurring, and instead of ignoring it (as I had done previously) I actually took it seriously.

The error told me that the /plugins/content and /plugins directories were writeable by group (ie. 777). Once I updated the permissions on the directories to 755 everything started working. It seems like Joomla's own security was causing this problem, preventing access to an open folder.

Thanks to silzenna for the help.