push & pull: <url> doesn't appear to be a hg repository

I'm trying to push and pull from my repo and I keep getting intermittent "abort: <url> does not appear to be an hg repository!" error messages. Sometimes it work, sometimes it doesn't. It's really annoying.

I'm not sure, but I have the feeling that it's related to the fact that I use a CNAME alias to refer to my repos.