Ubuntu 14.04.5 LTS upgrade to 16 fails via Software Updater

[Artem V L]

On the attempt to upgrade Ubuntu 14 to 16 via the Software Updater the following dialog window appears:

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 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

If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.

This dialog appears on the second step of the upgrade:
Preparing to upgrade [OK]
Setting new software channels <- Fails
...

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.13.0-95.142-generic 3.13.11-ckt39
Uname: Linux 3.13.0-95-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sun Sep 11 13:57:14 2016
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-10-25 (686 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-09-11 (0 days ago)
VarLogDistupgradeTermlog:

[Artem V L (artvl)]

I managed to perform the upgrade checking the logs (/var/log/dist-upgrade/apt.log) and solving the issues with "Broken" packages. However, it would be much better to have this step included into the upgrade asking a) whether to remove the packages that prevent the upgrade (and listing the packages) or b) skip the upgrade to manually solve the issue.

Moreover, after the upgrade I ended up with broken apt-get (it required libc, which required gcc-base) and had to manually download the libraries and install them via dpkg.
As it found, I was not the first who faced this issue, but it can be and should be considered during the upgrade process.

Thanks for your time and for the free Linux OS, hope this feedback helps to improve the reliability of the installation process.