20050RemoteAccessThe user DOMAIN\User connected to port VPN4-5 has been disconnected because no network protocols were successfully negotiated.
This error is logged on the computer running the Routing and Remote Access service when the client (who is trying to login) is not able to obtain a valid network address (e.g. IP address).
We had a working VPN setup which stopped working after we added an additional network adapter to the server running the RRAS service.
Open the "Routing and Remote Access" application, right-click the server name and select "Properties".
There, click the "IP" tab and ensure that the correct adapter is listed on the bottom. This adapter will be used to contact your DHCP server and relay IP addresses.
If that is already set correctly then make sure that the "IP address assignment" settings are correct as well.