If you can ping addresses on either side but can't ping the remote IPO then you probably don't have the correct IP route setup in the IP Office.

You should have a "default route" in each IPO pointed to the gateway for the LAN it is connected to.

Assuming 1 IP Office is on 192.168.1.0 network with watchdog router at 192.168.1.1 and another IP Office is on 192.168.2.0 network with it's watchdog router at 192.168.2.1...

IPO#1: IP: 0.0.0.0 Mask: 0.0.0.0 Gateway: 192.168.1.1
IPO#2: IP 0.0.0.0 Mask: 0.0.0.0 Gateway: 192.168.2.1