Comment 13 for bug 1510841

I also experience a similar/the same problem for upgrading from 14.04 to xenial. Indeed I do for several months now, always hoping that the bug would be fixed one day...
This is what pops up (in the end) when I sudo do-release-upgrade
"
Calculating the changes

Could not determine 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.
"
and here I am...

/var/log/dist-upgrade/apt.log tells me
"Broken dpkg:amd64 Breaks on software-center [ amd64 ] < 13.10-0ubuntu4.2 > ( gnome ) (< 13.10-0ubuntu9~)
  Considering software-center:amd64 -1 as a solution to dpkg:amd64 5881
  Added software-center:amd64 to the remove list" followed by a long list of this kind of broken statements and finally
"Can't install 'xubuntu-core' "

excerpt from /var/log/dist-upgrade/main.log:
2017-02-23 07:27:05,447 DEBUG Comparing 4.4.0-64 with 3.13.0-110
2017-02-23 07:27:05,482 DEBUG metapkg 'xubuntu-desktop' installed but marked_delete
2017-02-23 07:27:05,482 DEBUG none of the '['ubuntu-desktop', 'kubuntu-desktop', 'xubuntu-core', 'xubuntu-desktop', 'ubuntustudio-desktop', 'mythbuntu-desktop', 'kubuntu-netbook', 'lubuntu-core', 'lubuntu-desktop', 'ubuntu-gnome-desktop', 'ubuntu-mate-core', 'ubuntu-mate-cloudtop', 'ubuntu-mate-desktop']' meta-pkgs installed
2017-02-23 07:27:05,482 DEBUG guessing 'xubuntu-core' as missing meta-pkg
2017-02-23 07:27:05,482 ERROR failed to mark 'xubuntu-core' for install ("The cache has no package named 'xubuntu-core'")
2017-02-23 07:27:05,507 DEBUG blacklist expr 'xubuntu-desktop' matches 'xubuntu-desktop'
2017-02-23 07:27:05,507 DEBUG The package 'xubuntu-desktop' is marked for removal but it's in the removal blacklist
2017-02-23 07:27:05,616 ERROR Dist-upgrade failed: 'The package 'xubuntu-desktop' is marked for removal but it is in the removal blacklist.'
2017-02-23 07:27:05,617 DEBUG abort called

I am certainly running xubuntu. And it works, so I suppose that all necessary packages are installed. Unfortunately, just as for milvang, I do not understand what I need to do to be able to do the upgrade anyway. And I am not sure of the consequences if I remove xubuntu-desktop as proposed by rmjpraakash...