Route through VPN tunnel

[lorenzodv]

Please help me: this problem is driving me crazy.
I have two subnets: 192.168.1.0 and 192.168.2.0 connected through a pubblic
WAN.
I successfully enstabilished a VPN tunnel between 192.168.1.1 and
192.168.2.1.

Virtual addresses are the following:
192.168.1.1 10.0.0.1 VPN server
192.168.2.1 10.0.0.2 VPN client

Now, to join the two LANs, I need to route the subnet on the other end
thourgh the tunnel, right?
So...

route add 192.168.1.0 mask 255.255.255.0 10.0.0.2
(on the VPN client - works fine)

route add 192.168.2.0 mask 255.255.255.0 10.0.0.1
(on the VPN server - DOES NOT WORK)
(error: Parameter is incorrect)

Why Windows won't let me add the latter route? It would just send all the
traffic directed to the other subnet on the VPN interface, 10.0.0.1.
It seems I can't add routes through the 10.0.0.1 interface, no matter what
destination I'm trying to route and I can't find a reason for this!

I'm using Windows XP Pro: I know this is a Win2000 newsgroup but there is no
newsgroup about XP routing and I know that XP is based on 2000, so...

Thanks!