Losing external connectivity

I’m running SCO 5.0.6 and our primary application requires us to reboot daily. This box sits on an internal IP with NAT set up on the firewall to make the box accessible from the outside. Our firewall is set up as the default route. After the reboot, the box can?t see past our router (Cisco 678 on ADSL). It can see all internal ip’s fine, but I need to remove, then add the default route before the box can see the outside. Sometimes I need to remove/add the route a few times before I get a ping reply from an IP or name on the outside. DNS is working fine and this is the only machine with this problem on the network. Any ideas would be appreciated. Thanks!