do-release-upgrade doesn't work

I'm trying to upgrade Ubuntu from Precise to Quantal with do-release-upgrade, but I get an error; look at the following screencast: http://shelr.tv/records/4fff4ead9660807507000026
Also, it says that if you want to report the bug you should use the command "ubuntu-bug ubuntu-release-upgrader-core", but it doesn't work: I used "apport-bug `which do-release-upgrade`".

Thanks.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager-core 1:0.156.14.5
ProcVersionSignature: Ubuntu 3.2.0-26.41-generic 3.2.19
Uname: Linux 3.2.0-26-generic x86_64
ApportVersion: 2.0.1-0ubuntu11
Architecture: amd64
Date: Fri Jul 13 00:13:22 2012
GsettingsChanges:
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1342083749
 com.ubuntu.update-manager window-height 500
 com.ubuntu.update-manager window-width 600
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120402)
SourcePackage: update-manager
UpgradeStatus: Upgraded to precise on 2012-07-12 (0 days ago)
mtime.conffile..etc.update.manager.release.upgrades: 2012-04-03T22:10:11.594139