When you create a vpn client connection, the vpn server normally sends the ip address, mask, dns address etc to the client to use for te connection. In this case it is suggesting that the client has been told to use the google dns server which it is trying to do. If the client is trying to use 8.8.8.8 then it may depend on whether the client is setup to allow split tunnelling or not. I know that by default Cisco client software did not allow that, the result being that any attempt to contact an ip address outside the clients local network would be routed to the vpn server. If the vpn server was also the gateway to the internet then by default the cisco router did not allow incoming packets to be routed (they had to remain on the local network the router was on. Using a Draytek with the default MS client would allow split tunnelling so ip addresses on the internet could be contacted directly. In both cases control was governed by the vpn server and what it sent to the client.
The error message suggests that the client is trying to contact 8.8.8.8 but not through the vpn. It might be worth trying a tracert to see what route is being (or not) taken to the google dns server.
Is this affecting all or only some BT Internet users?
Are the affected users Mac users? Are the unaffected users Mac users?
