Can't upgrade from raring to saucy

[Martin]

I can't upgrade from raing to saucy.

Process abort with the following 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.

Thanks

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: ubuntu-release-upgrader-core 1:0.192.13
ProcVersionSignature: Ubuntu 3.8.0-35.50-generic 3.8.13.13
Uname: Linux 3.8.0-35-generic x86_64
ApportVersion: 2.9.2-0ubuntu8.5
Architecture: amd64
CrashDB: ubuntu
Date: Wed Feb 5 12:05:20 2014
InstallationDate: Installed on 2012-05-24 (621 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to raring on 2014-02-05 (0 days ago)