I have noticed this is a common problem. By googling Authentication failed, a lot of pages can be found but no one can help solve the problem.
I also notice a lot of similar questions have been closed here because they're considered to be too localized. But I do want to propose the moderators to give this issue a reconsideration. A lot of peole are stuck by this problem.
Below is the error message:
Authentication failed Authenticating the upgrade failed. There may be a problem with the network or with the server.
As with other people who also have the problem, I don't think there's anything wrong with my network connection.
Then I typed
and the error message is as below:
An unresolvable problem occurred while calculating the upgrade: E:Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages. This can be caused by: * Upgrading to a pre-release version of Ubuntu * Running the current pre-release version of Ubuntu * Unofficial software packages not provided by Ubuntu