agenor
After upgrading dokuwiki to 2016-06-26a "Elenor of Tsort" I was unable to access the dokuwiki at all
I created a new instance and then installed the plugins in my old instance into the new site, one by one
After installing hcalendar I had the same issue as my old instance.
Fixed the issue by deleting the hcalendar directory from /lib/plugins
Hope this helps