An unresolvable problem occurred while calculating the upgrade

[federico virello]

I tried to make the upgrade from Ubuntu 12.04 LTS to 14.04.2 LTS and during the calculation appeared the following error:
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.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.18
ProcVersionSignature: Ubuntu 3.2.0-77.112-generic-pae 3.2.66
Uname: Linux 3.2.0-77-generic-pae i686
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu17.8
Architecture: i386
Date: Sat Feb 21 05:58:29 2015
GsettingsChanges:
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1424494406
 com.ubuntu.update-manager show-details true
 com.ubuntu.update-manager window-height 709
 com.ubuntu.update-manager window-width 600
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100429)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: update-manager
Symptom: ubuntu-release-upgrader-core
UpgradeStatus: Upgraded to precise on 2015-02-21 (0 days ago)
VarLogDistupgradeTermlog:

[federico virello (virellof)]

Someone suggest this: "apt-get remove libkrb5-3" I'm going to try.