ubuntu 14.04 distro upgrade

[disconnect]

I'm using 14.04, and vanilla kernel on A20, followed the documentation for distro upgrade, but it's in endless loop:

 

Calculating the changes


Error authenticating some packages


It was not possible to authenticate some packages. This may be a
transient network problem. You may want to try again later. See below
for a list of unauthenticated packages.


module-init-tools




Restoring original system state

After this appears, the whole dist upgrade process restarts, and ends with the same error.