VPN Clients Can’t Talk to DNS

I have a OS X Server 10.6 setup as a router with Ethernet 1 plugged into my ISP with a public IP and Ethernet 2 with the IP 192.168.16.1 this machine has DHCP, DNS, NAT, and VPN services running on it. My problem is that anyone that VPNs into this server for some reason cannot talk to the DNS server that is running on the same machine. In the log for the DNS service I occasionally see the following error: client 192.168.16.240#59719: view com.apple.ServerAdmin.DNS.public: error sending response: host unreachable 192.168.16.240 is the IP of the VPN connection I was running at the time I was trying to resolve a DNS record that is only stored on that machine. The VPN service is configured to use 192.168.16.1 for the DNS server and that is the IP that shows up in the VPN connection settings on the client so I don't know what is keeping the client from talking to the DNS service. Also note that I able to both ping and access shares for all the machines on the private network by their IP, it is only resolving the DNS names that doesn't work.