Windows VPN not authenticating from ADSL to Wireless link

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http://serverfault.com – I have a normal windows VPN on a computer connecting to a 196.201.x.x/24 IP. If this VPN tries to connect from any address in the 41.x.x.x range it cant get there. The server is a normal windows 2008 server, running exchange with a PPPoE IP natted to a public IP on the public gateway of the wireless network as the server is on site and its connectivity is derived from Mikrotik RB's. The computer on the 41 range can traceroute and ping the server, but the VPN does not authenticate. When on the network or any other, the VPN works fine. Is there something that could be configured on the VPN clie (HowTos)