The eth0 was renamed to eth1 due to change of Network Adapter MAC-address. If you know your previous MAC, you can edit VM configuration and set NetworkAdapter to use old MAC. This should make network interface be eth0 back.
The change of MAC address could occur while converting VM from 3.0 to 4.0 on build 3522 (there should not be such behaviour on build 3540)
The behaviour
ifup eth1 returns "Ignoring unknown interface ...."
seems logical, since afaik there are scripts like ifup-eth0/ifdown-eth0, which are created while configuring system. So ifup eth1 cann't find the script ifup-eth1 and barks.
Interface may be started manually. Probably, by command "sudo /sbin/dhclient eth1"...
So, either eth1 need to be configured somehow (using some your linux distro utility), or MAC address should be changed to the previous address (which will make it back eth0)
Last edited: Dec 12, 2008