Problem: If you have a web-server with Server 2008 as operating system, you may experience very slow connections to the hosted website and errors in rdp sessions saying that there was a protocol error.
Reason: In Server 2008 IPv6 is enabled by default. This may lead to connection problems and unavailability of hosted services from other systems.
Solution: To solve these problems disable IPv6 on the server.
Attention: If you just uncheck the IPv6 check-box on your network card, you do not disable IPv6. To do so open registry go to the following hive HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\. There should be a key called “DisabledComponents” if so change it’s value to “FF” in hex. If it does not exist, create a new DWORD Key with the value “FF” After you did so, reboot the server and check if the performace has increased.

Source: Microsoft KB Article