Please make sure that you run the latest 10.0.1 version, there have been some issues with some WebDAV clients. If there is still a problem, you can try this fix:
If you don’t succeed, you can check the whole webdav-setup with a litmus test (there is a howto on forum.owncloud.org). I also remember some longer debugging with lightspeed setups, I don’t remember if we found a solution.