Upgrade to 12.04 Failed

[Sasa Stamenkovic]

I run upgrade after installing all recommended updates from update manager, and I got dialog:

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 update-manager' in a terminal.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: update-manager 1:0.152.25.9
ProcVersionSignature: Ubuntu 3.0.0-17.30-generic 3.0.22
Uname: Linux 3.0.0-17-generic i686
NonfreeKernelModules: fglrx
ApportVersion: 1.23-0ubuntu4
Architecture: i386
Date: Thu Apr 26 18:54:55 2012
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: Upgraded to oneiric on 2012-04-26 (0 days ago)

[Sasa Stamenkovic (umpirsky)]

Now tried:

umpirsky@umpirsky:~$ sudo apt-get update
...
Fetched 16.6 kB in 1min 22s (200 B/s)
Reading package lists... Done
W: GPG error: http://archive.canonical.com oneiric Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <email address hidden>

Any idea?