apt packagekit backend error

[marcobra (Marco Braida)]

Description: Ubuntu karmic (development branch)
Release: 9.10

ubuntu@ubuntu:~$ apt-cache policy apt
apt:
  Installato: 0.7.21ubuntu1
  Candidato: 0.7.21ubuntu1
  Tabella versione:
 *** 0.7.21ubuntu1 0
        500 http://archive.ubuntu.com karmic/main Packages
        100 /var/lib/dpkg/status
ubuntu@ubuntu:~$

apt-cache policy packagekit
packagekit:
  Installato: 0.4.8-0ubuntu5
  Candidato: 0.4.8-0ubuntu5
  Tabella versione:
 *** 0.4.8-0ubuntu5 0
        500 http://archive.ubuntu.com karmic/main Packages
        100 /var/lib/dpkg/status

i'm running a terminal sudo apt-get update then i get this error window (see the attached image)... then apt-get update process became very slow to finish...

Error Type: <type 'exceptions.AttributeError'>
Error Value: 'PackageKitCache' object has no attribute '_dict'
  File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 1966, in <module>
    main()
  File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 1963, in main
    run(args, options.single)
  File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 1925, in run
    backend.dispatcher(args)
  File : /usr/lib/python2.6/dist-packages/packagekit/backend.py, line 632, in dispatcher
    self.dispatch_command(args[0], args[1:])
  File : /usr/lib/python2.6/dist-packages/packagekit/backend.py, line 540, in dispatch_command
    self.get_updates(filters)
  File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 653, in get_updates
    for pkg in self._cache.getChanges():
  File : /usr/lib/python2.6/dist-packages/apt/cache.py, line 164, in getChanges
    for p in self:
  File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 196, in __iter__
    for pkgname in sorted(self._dict.keys()):

Thank you