Most likely caused by a misconfiguration on webserver side which doesn’t allow to use some specific HTTP verbs (in this case most likely DELETE). The following FAQs [1] and [2] are containing all needed info how to verify that your webserver is configured correctly.
[1]
If you encounter the following scenario:
You can access your owncloud web interface
The owncloud sync client as well as WebDAV (via some WebDAV client, or a direct access in a browser via http://yourowncloud/remote.php/webdav ) aren’t working (typically you will see a 401/403/405 error in the logs)
You’re getting a message “Your web server is not yet properly setup to allow files synchronization because the WebDAV interface seems to be broken. Please double check the installation guides.”
Ther…
[2]
litmus is a WebDAV test suite to test your webserver for all needed WebDAV methods which could help you debugging WebDAV problems like described in this FAQ: https://forum.owncloud.org/viewtopic.php?f=17&t=7536
The test suite is available here:
http://www.webdav.org/neon/litmus/
but is fairly old (latest release 9 December 2011) and needs some steps to get it to work on Debian when testing SSL enabled webservers:
1. Download sources
Download and extract the sources from the link above …