Netopia R910: Router -to-Router VPN, Can't PING Remote LAN

I have successfully set up a router - router VPN between two Netopia R910 routers using the documentation provided at the Netopia website.

There is one PC connected directly to each Netopia router at each location and each router is also connected to the LAN via an Ethernet cable plugged into a wall jack-plugged into the switch.

However, I am unable to browse the remote network at either location. I can ping the machines directly attached to each Netopia router, but I can't ping, for example, the Unix server on the remote LAN or the Windows server for that matter - or any of the PCs for that matter.

I CAN ping the internal IP address of the routers FROM the LAN at each location.

Can anyone help me with this? What could I be missing? Any input would be greatly appreciated.

Thanks in advance.