iI cannot upgrade ubuntu 12.04 to 12 .10

[renjunairpr]

whenever i am trying to updgrade ubuntu to 12.10i am ghetting this message

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade:
E:Unable to correct problems, you have held broken packages.

 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.

i am using toshiba satellite c640 i am using ubuntu in standalone
hope u will fix this

with regards

renju

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.11
ProcVersionSignature: Ubuntu 3.2.0-35.55-generic-pae 3.2.34
Uname: Linux 3.2.0-35-generic-pae i686
ApportVersion: 2.0.1-0ubuntu15.1
Architecture: i386
Date: Sun Dec 23 22:28:30 2012
GsettingsChanges:
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1356280918
 com.ubuntu.update-manager show-details true
 com.ubuntu.update-manager window-height 597
 com.ubuntu.update-manager window-width 901
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_IN:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_IN
 SHELL=/bin/bash
SourcePackage: update-manager
Symptom: ubuntu-release-upgrader-core
UpgradeStatus: Upgraded to precise on 2012-12-23 (0 days ago)
VarLogDistupgradeAptclonesystemstate.tar.gz: Error: [Errno 13] Permission denied: '/var/log/dist-upgrade/apt-clone_system_state.tar.gz'
VarLogDistupgradeTermlog:

[Brian Murray (brian-murray)]

Reviewing the files from your upgrade attempt you seem to have enabled the xorg-edgers-ppa. This will prevent the upgrade as that PPA contains different versions of packages essential to Ubuntu. The page, https://launchpad.net/~xorg-edgers/+archive/ppa, contains details on to how to revert to the official Xorg packages.