Can't upgrade to ubuntu 13.10

[Viktor]

When running the upgrade it stops and says:

Could not determine 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 13.04
Package: ubuntu-release-upgrader-core 1:0.192.13
ProcVersionSignature: Ubuntu 3.8.0-33.48-generic 3.8.13.11
Uname: Linux 3.8.0-33-generic i686
ApportVersion: 2.9.2-0ubuntu8.5
Architecture: i386
CrashDB: ubuntu
Date: Sun Nov 24 15:27:30 2013
InstallationDate: Installed on 2012-02-26 (637 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha i386 (20120218)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to raring on 2013-11-24 (0 days ago)
VarLogDistupgradeTermlog:

[N1ck 7h0m4d4k15 (nicktux)]

Thank you for taking the time to report this bug and trying to help make Ubuntu better. However, it seems that the third reason is applied.
  (* Unofficial software packages not provided by Ubuntu)

You have external sources enabled (like PPAs) and the upgrade could not continue.

Please read some answers as a guide on how to upgrade your Ubuntu installation without problems.
http://askubuntu.com/questions/203301/how-to-safely-upgrade-from-an-older-ubuntu-version-to-a-newer-one

Best Regards
    NikTh