Why will VPN Not work

I am attempting to set-up a simple VPN connection into my Home office. I have an ADSL conncetion to the internet with a static ISP address.
The router is connected to a Hub into which my Windows 2000 server and other PCs are connected.
All have internet access as the router is configured for nat and is the default gateway.

The router has been set to forward all port 1723 and 1701 traffic to the server.

I have configured the Windows Routing & Remote Access as advised, but when I attempt a VPN connection the message Verifying User Name and Password stays on the screen. The sever Event log tells ne that the attempted connection timed out in authentiction.

This problem is driving me mad.

Any help would be appreciated.