ensure that the protocol 47 is allowed through the firewall and forwarded to VPN server if needed...
not too sure what your trying to do and I havent used mandrake so yeah... dont even know if its a firewall issue
I use iptables on my gateway to forward to VPN... im guessing that MNF uses a firewall
# Redirect VPN Traffic
$IPTABLES -t nat -A PREROUTING -i $OUTSIDE -p tcp -m tcp --dport $VPN_PORT -j DNAT --to $VPN_IP:$VPN_PORT
$IPTABLES -t nat -A PREROUTING -i $OUTSIDE -p 47 -j DNAT --to $VPN_IP
# VPN
$IPTABLES -A INPUT -i $OUTSIDE -d 0/0 -p tcp -m tcp --dport 1723 -j ACCEPT
$IPTABLES -A INPUT -i $OUTSIDE -d 0/0 -p 47 -j ACCEPT
so check that all needed ports/protocols are open
hope that helps