iface lo inet loopback
# This is a list of hotpluggable network interfaces.
# They will be activated automatically by the hotplug subsystem.
# The primary network interface
iface eth0 inet static
iface eth1 inet static
this is actually incorrect and will cause two symptoms. When you run /etc/init.d/networking restart you get this response:
RTNETLINK answers: no such process
Your internal network will work ok and you'll be able to access the system but you will not be able to get to the outside network and a ping to google.com will come back with unknown host.
The solution is to remove the second gateway listing (highlighted in red). You only need one. Run /etc/init.d/networking restart and you should be good to go.