Are you using 3G Modems such as Huawei E220, Sierra Air Card, and others? I’m pretty sure that you can’t open some of the web sites. You can test this by going to http://support.microsoft.com and see if you could open the site.

Some people experience very slow overall internet connection and you’re not reaching the published speed of your 3G provider.

Now, I have good news for you. It’s a bug and it can be fixed. It’s a registry tweak that will adjust the Maximum Transmission Unit (MTU) of Windows that’s just right for 3G connection. In layman’s term, it sets the maximum data it can sends at a time.

Just download this registry file http://rapidshare.com/files/209179082/PPP___Tunnel_MTU.reg and merge it with your registry.

By the way, this only works for Windows 2000, Windows XP, and Windows Vista.