Comment 1 for bug 47533

https://launchpad.net/distros/ubuntu/+source/update-notifier/+bug/29295

Following the instructions from this bug report to do a change to some permisions has fixed this issue for me, I had the same issue when upgrading from breezy -> dapper.

Some developers seem fit to think I have made a permission change originally myself, when I know I havent :)