do-release-upgrade -d failed(from 14.04 to 16.04-testing)

[Ergil Osin]

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

Calculating the changes

Calculating the changes

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.13.0-77.121-generic 3.13.11-ckt32
Uname: Linux 3.13.0-77-generic i686
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: i386
CrashDB: ubuntu
Date: Tue Feb 16 17:40:18 2016
InstallationDate: Installed on 2012-09-03 (1261 days ago)
InstallationMedia: Ubuntu-Server 12.04 LTS "Precise Pangolin" - Release i386 (20120424.1)
PackageArchitecture: all
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-02-16 (0 days ago)