I see the problem now (I have been poking around for about 10 minutes). You are trying access this page through HTTPS (port 443) when it is not available on this port (although it is available through HTTP - port 80). I don't think this site is very secure, as it expects people to log on using an unencrypted connection. It is strange that the server is still listening on port 443 though.

If you are getting this error message after you log in (they switch you over from HTTP to HTTPS) then I suggest you re-enter the web address with http:// at the front (although they may still redirect you to HTTPS, meaning this won't work).

If your using proxy some times server may not respond.

orange Firefox button (or Tools menu) > Options > Advanced > "Network" mini-tab > "Settings" button

The default is "Use system proxy settings"

try it now

I agree with iamjayakumars. Using proxy sometimes the server takes too long to respond or doesn't respond at all so try Changing your proxy settings. It might help you.

Now I get a 404 error using HTTP as well, and the root is forbidden (error 403).

I was skeptical that the proxy settings would be causing the problem, but I tried changing them anyway and no difference. The 404 error page comes back reasonably quickly, so I'm not sure that the respond time is the problem here.

yes few browser setting may also help you just try to change some advance setting.