System updater can't calculate the upgrade

[Petka]

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

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: ubuntu-release-upgrader-core 1:0.192.13
ProcVersionSignature: Ubuntu 3.8.0-31.46-generic 3.8.13.8
Uname: Linux 3.8.0-31-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.9.2-0ubuntu8.3
Architecture: amd64
CrashDB: ubuntu
Date: Thu Oct 17 22:42:46 2013
InstallationDate: Installed on 2012-05-03 (531 days ago)
InstallationMedia: Kubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120423)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to raring on 2013-10-17 (0 days ago)