could not determine the upgrade

[Obeta]

I was updating ubuntu version 12 to the latest realese version 14.04.1 LTS. Each time I attempted to upgrade I will always get this error message:
Could not determine the upgrade
an unresolvable problem occurred whilecalculating the upgrade
This can be cause by:
updating 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 these applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core'

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.17
ProcVersionSignature: Ubuntu 3.2.0-74.109-generic 3.2.64
Uname: Linux 3.2.0-74-generic x86_64
NonfreeKernelModules: nvidia wl
ApportVersion: 2.0.1-0ubuntu17.8
Architecture: amd64
Date: Fri Dec 26 01:08:33 2014
GsettingsChanges:
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1419445276
 com.ubuntu.update-manager window-height 518
 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 2014-12-24 (1 days ago)
VarLogDistupgradeTermlog: