Thanks.
It works here as well. It was a firewall issue.
Now I'm trying to find a way to play my music library remotely (outside my network) on the speakers connected to the network where I am e.g. my friend's house). I see instead the list of the speakers conected to my local network at home.
If you using another instance of MC, just play to its player zone. If you are playing to devices on the network at your remote location you should still just see them in your zone list (along with the there: zones from your house) if you are on the wifi network at your remote location.
If you don't want to see your home zones on the client, under the clients Settings, Media Network, Client Options you can unclick the option "Show playback zones from the server on the client"