If I'm reading into this correctly, you dial-up to the internet then establish a VPN connection (point-to-point tunnel) to the RAS server on your network. Is that correct?
If so, disable the "use default gateway on remote network" setting on the "PPP TCP/IP" configuration page for your VPN connection.
With this setting enabled, all network traffic will be routed through the VPN to the remote network server, including DNS requests for internet IP addresses. This may be blocked by the RAS server, or may simply take too long to process before your PC stops waiting and displays an error message.