Error "---> System.Xml.XmlException: 'Element' is an invalid XmlNodeType." in Logging of iCloud CalDav account

When I try to sync with my iCloud caldav i get the error message
—> System.Xml.XmlException: ‘Element’ is an invalid XmlNodeType.

How can I solve this ? I tried almost everything to sync my caldav iCloud account with the calendar of my iPhone, but until now it does not sync.