cant upgrade 11.04 to 11.1 "An unresolvable problem occurred while calculating the upgrade:"

[Peter Hawkins]

Description: Ubuntu 11.04
Release: 11.04

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: update-manager 1:0.150.4
ProcVersionSignature: Ubuntu 2.6.38-12.51-generic 2.6.38.8
Uname: Linux 2.6.38-12-generic x86_64
Architecture: amd64
Date: Tue Oct 25 13:02:15 2011
GConfNonDefault:
 /apps/update-manager/check_new_release_ignore=
 /apps/update-manager/first_run=false
 /apps/update-manager/show_details=true
 /apps/update-manager/window_size=(600,600)
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=de_DE:en
 PATH=(custom, user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: Upgraded to natty on 2011-10-25 (0 days ago)