In some cases the MTU for both the Ethernet adapter and the PPPoE adapter must be configured. Try setting the MTU on the Ethernet adapter to 1400 using the SetMTU utility included with the VPN client. The MTU for the PPPoE connector can usually set b...
It's hard to say what might be wrong. Something is obvously missing or misconfigured. Have you tried using traceroute to determine what path the traffic is attempting to take? That should at least tell you whether the your route is being used or not.