If you just upgraded ownCloud on Ubuntu 15.10 to version 9 (using
apt-get dist upgrade), you probably get the error message shown above. Adding
/index.php manually still redirects to the ownCloud login screen.
As mentioned here open
/var/www/owncloud an comment out
RewriteRule .* index.php [PT,E=PATH_INFO:$1]
and restart apache with
service apache2 restart