I sometimes have this problem too, but for some reason I was connected to the server trough my internet's proxy settings. Make sure you have a direct connection with the service. In my case I had to enable the UPnP port on my router, which is neccesary to let it work properly. Also you can enable the virtual servers, which is easy to select in a belkin router. Now it's gone at mine. Agree with the webmessenger hint. I used it a couple of times too
. Good luck...