No changes have been made since last login to my cloud.
But today -> Adminitration Settings -> same error.
Remarked that the URL https://owncloud.org is “broken” too (has in different browsers (Chromium, Firefox, IE) an invalid https certificate … hint on HSTS
There are issues with the site’s certificate chain (net::ERR_CERT_DATE_INVALID).
Any solution (putting e.g. a ca-certificate.cert into the owncloud/config directory) doesn’t work!