If you try open a website (for example m.google.com) on your BlackBerry device you will see the following error:

HTTP Error 400: Bad Request

The server could not understand the page request, or they could not process any other reason. Load a different page.

If you press on details you see:

Connection refused

m.google.com:80

If this happen for more then one user go to your BlackBerry (BES) Server and check if the Proxy config if it is valid.

A possible problem might be: You configured the MDS to use a config.pac file. But if you try to open the config.pac via webbrowser your proxy server said:

Forbidden

You don't have permission to access /config.pac on this server.

In that case you need to check the proxy config and restore that file!