upgrade doesn't complete from 12.04 to 14.04

[Alaa Mohammed Agwa]

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

this appeared to me while upgrading

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.13
ProcVersionSignature: Ubuntu 3.2.0-61.92-generic 3.2.55
Uname: Linux 3.2.0-61-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu17.6
Architecture: amd64
Date: Fri Apr 25 20:20:53 2014
GsettingsChanges:
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1398449840
 com.ubuntu.update-manager window-height 572
 com.ubuntu.update-manager window-width 600
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 SHELL=/bin/bash
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
SourcePackage: update-manager
Symptom: ubuntu-release-upgrader-core
UpgradeStatus: Upgraded to precise on 2014-04-25 (0 days ago)
VarLogDistupgradeTermlog:

[Brian Murray (brian-murray)]

This is likely related to some PPA packages you have enabled and installed.