not able to upgrade from 14.04 to 16.04.1

[mahesh]

While updating ubuntu 14.04 to 16.04.1............

$sudo do-release-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
Building data structures... Done

[Brian Murray (brian-murray)]

Thanks for taking the time to report this bug and helping to make Ubuntu better. Could you please add the log files from '/var/log/dist-upgrade/' to this bug report as separate attachments? Thanks in advance.

[Launchpad Janitor (janitor)]

[Expired for ubuntu-release-upgrader (Ubuntu) because there has been no activity for 60 days.]