Comment 8 for bug 407302

your network always has to be configured, though it sounds like you are used to it being autoconfigured. I suspect that the network in general is autoconfed at least with network-manager and by the installer. If you don't use network-manager to configure your network, then /etc/network/interfaces will be used (and vis a versa).

I'm looking at my interfaces file (jaunty) and it isn't configured even for dhcp, so I wouldn't expect it to work without network-manger or some sort of configuration. It might be a change from previous releases?

So I think you should check your interfaces. BTW, I gave the wrong location, it is /etc/network/interfaces

gl!