I did further testing: The message went away with both current Ubuntu kernel (3.2.0-31-virtual) and mainline kernel (3.6.0-030600-generic #201209302035) on my machine as well, once I removed the IPv6 gateway configuration in /etc/network/interfaces.
/etc/network/interfaces: iface eth0 inet6 static address 2001:638:a000:4104::228 netmask 64
Hope this helps.
I did further testing: The message went away with both current Ubuntu kernel (3.2.0-31-virtual) and mainline kernel (3.6.0- 030600- generic #201209302035) on my machine as well, once I removed the IPv6 gateway configuration in /etc/network/ interfaces.
/etc/network/ interfaces: a000:4104: :228
iface eth0 inet6 static
address 2001:638:
netmask 64
Hope this helps.