Comment 5 for bug 97451

I have what might be the same problem. pppoeconf works the first time then fails after 2 restarts. I undo the modifications of pppoeconf to /etc/network/interfaces and run it again. Works, then fails after 2 restarts.

I try from live CD and the Network manager works, so I reinstall ubuntu, network manager does not work. I go back to liveCD, network manager no longer works.

Let me add that I think it is a problem with avahi. Every time it works the only interface that shows up is "eth0", but when it fails it usually ends up stalling for a bit while it creates "eth0:avahi".