Nov 13 10:10:10 my_machine kernel: [ 1000.101010] eth0: IPv6 duplicate address detected!
Then it's obviously Friday 13th and you should put it down to ....Yeah maybe but yesterday it was the same last week....It seems there's a kernel (2.6.31-15) bug which means IPv6 Duplicate Address Detection (DAD - see RFC4862) is generating false-positives and subsequently not permitting your global address to be assigned to an interface.
To work around this bug do (change eth0 to your iface name):
sudo sysctl net.ipv6.conf.eth0.accept_dad=0