iptables and openvpn

[markw-FJ05HQ0HCKaWd6l5hS35sQ at public.gmane.org (markw-FJ05HQ0HCKaWd6l5hS35sQ at public.gmane.org)]

I'm having a bit of an issue. I'm pretty good at openvpn but I only know
just enough about iptables to get most simple things done.

Here's my setup:

Server A is on a 10.x.x.x network. (LanA)
Server A is connected to the internet
Server A runs openvpn as a server

Server B is on a 192.168.x.x network (LanB)
Server B is connected to the internet and serves as the firewall/gateway
for LanB and works flawlessly.
Server B runs openvpn as a server

Currently, a computer can connect to either system through openvpn and
access their respective networks just as you would expect. It all works.
The SSL, certs, keys, basic forwarding, etc. work perfectly.

On LanB, all the computers go through Server B for non-local IP addresses.
I would like to run an openvpn client on Server B to connect to Server A
through the internet and make the 10.x.x.x remote LAN available on LanB.

Right now, I can (from any machine on the 192.168.x.x net) type "ping
10.1.10.xx" and (with openvpn in verbose mode on Server B) see the "Wr"
handshake of the ping, but it never gets back to the 192.168.x.x machine,
it dead-ends on Server B.

On Server B, "ping 10.1.10.x" works as you would expect.

So, the routing works. The 192.168.x.x machines are going to the gateway
correctly. The gateway is sending the ping over openvpn correctly. The
openvpn connection is working correctly. The final step of getting the
packet from the server mack to the machine is failing.

What am I missing?