I found the solution of my problem.
Curiously, in ezurlalias table, the main node (node_id: 2) wasn't have a destination_url. (o_O) If this was not a problem for browsing in the back office, webdav can't accessing to the destination of "Content". I don't know why this problem arrived suddenly and how my main node_id lost the destination_url, but it was the origin of my problem.
PS: In fact, I confirm we can use webdav with eZ Publish in cluster mode.
