dav:// not working with my webdav server, while other clients work fine

["Ben Davis" <bendavis78 gmail com>]

Hi all.  I'm testing out my PHP-based webdav server with different clients,  and gnome-vfs seems to be the only one not working.   I've tried  windows, cadaver, and davfs2, and they all seem to work fine.   When I enter the same url (with dav:// instead of http://) in nautilus,  it just gives me this error:

The folder contents could not be displayed
"webdav" could not be found. Perhaps it has recently been deleted.

What is a good way for me to debug this?  I'd like to see what is causing nautilus or the webdav module to return this error, and any debug messages would be helpful, but I don't know where to start.   Any ideas?