I have no firewalls rules established, I’m using the default rules that zeroshell installs with as it is only being used as a router and VPN concentrator. Also, the netmasks are correct for all systems on the internal subnet (255.255.255.0). I have checked both the router and the virtual servers.
One other thing that might help troubleshoot is that all of these systems are running on host-only networks on VMWare Server 2.0, on Ubuntu 9.04. However all of the virtual servers can ping each other and the host within the host-only internal network without any problems, only the Zeroshell virtual image does not respond until it sends out the first ping. The Zeroshell router is bridged to an external ethernet interface and provides external connectivity (gateway) and VPN access to the host only network.
Could this be ARP related?