I'm wondering if someone has met these problems:
when i run "ufw enable" the console tell that Errors with init script,
but if i run a second time,no errors appear.
But i can not set "ufw default deny" untill i disable ufw.
If i reboot i can see some errors with ufw.I enable "ipv6=yes" in /etc/default/ufw,i can't connect to any ipv4 networks.

Finally i solve the problem by add debian sid source and update the two packages related and the problem solved.And it seems that no new problems appear.
It's my experience,hope it'll be helpful