Setup Failure Codes/Suhosin "server.strip" disabled
The page identifies a major configuration problem. DAViCal might appear to work somewhat but major functionality will be broken until this is resolved.
The "Suhosin" extension to PHP is a commonly installed security thing. We recommend it, because it makes PHP 'safer' and that must be important, right?
Unfortunately it gets a little over the top (and OK, maybe DAViCal does push the boundaries of what a "web app" would be expected to do :-), but you should know that if you have this particular option enabled then DAViCal *will* be broken.
This page is all a bit vague, and that's partly because the Suhosin Configuration page on their website doesn't actually detail this option. Perhaps it's an old, ill-thought-out misfeature that has been discontinued.
Add the setting below to your php.ini file or your virtual host configuration file:
php_admin_flag suhosin.server.strip off
Since this setting is a php_admin_* setting it cannot be used in .htaccess or ini_set.