Problem upgrade 15.10 to 16.04

Question

I do this to upgrade 15.10 to 16.04:

    $ sudo apt-get update
    $ sudo apt-get dist-upgrade
    $ sudo do-release-upgrade

and after download from xenial repositories, show me this:

Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done

Calculating the changes

Calculating the changes

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.


Restoring original system state

Aborting
Reading package lists... Done
Building dependency tree
Reading state information... Done
=== Command detached from window (Sun Apr 24 23:59:43 2016) ===
=== Command terminated with exit status 1 (Sun Apr 24 23:59:53 2016) ===

I reported the bug to ubuntu wbsite.
Any idea to fix this problem and upgrade to 16.04?

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I found this and my problem is solved now :) Try executing:

grep ERROR /var/log/dist-upgrade/main.log

Hopefully this will show you the names of conflicting packages. For me it was (I broken long line to be easier to read):

2014-10-25 18:15:05,915 ERROR Dist-upgrade failed: 
    'The package 'postgresql-9.3-postgis-2.1' 
    is marked for removal but it is in the removal blacklist.

postgresql-9.3-postgis-2.1 is conflicting package here. It will probably be different one or some for you. You can then remove it/them by:

sudo apt-get remove conflicting-package-1 conflicting-package-2 ...

Then just restart distribution upgrade.

inhere