cannot upgrade to 14.04

[Sol Schvartzman]

I am trying to upgrade from version 12.04 LTS to 14.04.2 LTS. It does the Preparing to Upgrade step but it stops at the next one: Setting new channel software and it returns the message:

"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."

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.18
ProcVersionSignature: Ubuntu 3.2.0-77.114-generic 3.2.66
Uname: Linux 3.2.0-77-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.8
Architecture: amd64
Date: Thu Mar 19 14:48:24 2015
GsettingsChanges:
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1426772841
 com.ubuntu.update-manager window-height 532
 com.ubuntu.update-manager window-width 600
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: update-manager
Symptom: ubuntu-release-upgrader-core
UpgradeStatus: Upgraded to precise on 2015-03-19 (0 days ago)
VarLogDistupgradeTermlog:

[Ubuntu Foundations Team Bug Bot (crichton)]

You seem to have installed the cinnamon package on Ubuntu 13.10. Unfortunately, that package is not available yet for 14.04. To upgrade to Ubuntu 14.04 LTS you'll need to either wait for a fix for cinnamon to be available or uninstall the package and then upgrade.

[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]