VPN setup Hel--L2TP Security Negotiations times out

OK we have the following setup
Linksys WRT54G Wireless-G Router that supports VPN Pass through
It is setup in Security settings to the following:

ALL THE FOLLOWING ARE DISABLED
Block Anonymous Internet Requests
Filter Multicast
Filter Internet NAT Redirection
Filter IDENT (Port 113)

ALL THE FOLLOWING ARE ENABLED
IPSec
PPTP
L2TP

We have win 2003 domain controller(controller.domain.com) which has a user
setup
to be allowed for dial-in access.

Second win 2003 server (vpn_server.domain.com) is member of the domain but
is not a dc. It has Routing and Remote
Access installed on it and running. Authentication settings for VPN are set
to Windows Authentication.

Windows firewall isn't running on eiher server.

Now I used to be able to connect to the network with VPN but am unable to do
so now.
I can ping WAN port on the router. What else do I need to do to troubleshoot
the problem?

VPN connection 'says connecting to network.com' then says
"Error 792: L2TP connection attempt failed because security negotiation
timed out"

A few more questions:
Do I need 2 network cards on the VPN server?
Do I need to setup port forwarding on linksys for the VPN server?
If not how does VPN traffic find it's way to the machine?

Thanks a million for all the wonderful replies.