In my case, uninstalling KB935839, KB935966, KB933566, KB935840, KB927891, KB926122 and restarting the server was the solution to this problem. The VPN now works like before.
From a newsgroup post: "What protocols do you have configured for RAS? Do you have NetBEUI configured? If so try this:
1. Disable NetBEUI on the external adapter.
2. Disable NetBIOS over TCP/IP on the external adapter.
3. Disable NetBEUI on the RAS/VPN interface/connection".
For troubleshooting a connection that uses L2TP check ME259335
and the link to Connecting Remote Users Across the Internet Using L2TP.
Our server has 2 NIC's (public & private) and is configured to use NAT within Routing & Remote Access. We had disabled the DLC, IPX and NetBEUI protocols on the public NIC since we did not need those protocols on the public side of the network. When the server was rebooted we started getting the errors. Once the protocols were re-enabled and the server rebooted the errors were gone.
This is based on the fact that your VPN connections are using NetBEUI. If you enable them to access the entire network, you get this error. If you allow them only access to this computer, you won't receive this error.
I was getting this error because I swapped out a nic on a win2k server and after that RRAS wouldn't start. When I enabled the Remote Registry Service RRAS came up.
It may be a good idea to use one protocol on the private NIC, and another protocol on the public NIC. In this way, the threat of an unauthorised access to the internal network is minimised. I think it is safe to just ignore the error message.