Sometimes [ Error connecting to VPN – Error 800 : Unable to establish the VPN connection. The VPN server may be unreachable, or security parameters may not be configured properly for this connection ] comes out under Windows XP when attempt to establish a VPN connection, connection that is working and worked just fine all the time. The problem comes from [ Routing and Remote Access ] service, which for unknown reasons it works but not as expected, even is not reporting any error or is not stopped. This problem can be solved without restarting the computer, by simply restarting the [ Routing and Remote Access ] service.
Start > Control Panel > Administrative Tools > Services > browse and select [ Routing and Remote Access ] and click on Restart the service.
Service name: RemoteAccess
Dispaly name: Routing and Remote Access
Description: Offers routing services to businesses in local area and wide area network environments.
Path to executable: C:\WINDOWS\system32\svchost.exe -k netsvcs