Comment 19 for bug 613412

I'm experiencing the same problem in Oneiric.

Deleting /etc/apt/apt.conf.d/20packagekit made the error message go away.

I did have packagekit-backend-aptcc installed.

I'm going to reinstall packagekit and see if that fixes things...

(reinstalling via "apt-get install --reinstall")

Hmm.. It didn't re-create the /etc/apt/apt.conf.d/20packagekit file.

(apt-get purge packagekit; apt-get install packagekit)

Now it's back. Gonna install packagekit-backend-smart as suggested:

sudo apt-get install packagekit-backend-smart
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
  python-smartpm smartpm-core
The following NEW packages will be installed:
  packagekit-backend-smart python-smartpm smartpm-core
0 upgraded, 3 newly installed, 0 to remove and 1 not upgraded.
Need to get 357 kB of archives.
After this operation, 3,121 kB of additional disk space will be used.
Do you want to continue [Y/n]?
Get:1 http://us.archive.ubuntu.com/ubuntu/ oneiric/main python-smartpm i386 1.4-1ubuntu1 [331 kB]
Get:2 http://us.archive.ubuntu.com/ubuntu/ oneiric/universe smartpm-core i386 1.4-1ubuntu1 [4,760 B]
Get:3 http://us.archive.ubuntu.com/ubuntu/ oneiric/universe packagekit-backend-smart i386 0.6.15-1build1 [20.7 kB]
Fetched 357 kB in 2s (159 kB/s)
Selecting previously deselected package python-smartpm.
(Reading database ... 580070 files and directories currently installed.)
Unpacking python-smartpm (from .../python-smartpm_1.4-1ubuntu1_i386.deb) ...
Selecting previously deselected package smartpm-core.
Unpacking smartpm-core (from .../smartpm-core_1.4-1ubuntu1_i386.deb) ...
Selecting previously deselected package packagekit-backend-smart.
Unpacking packagekit-backend-smart (from .../packagekit-backend-smart_0.6.15-1build1_i386.deb) ...
Processing triggers for man-db ...
Processing triggers for packagekit ...
Setting up python-smartpm (1.4-1ubuntu1) ...
Setting up smartpm-core (1.4-1ubuntu1) ...
Setting up packagekit-backend-smart (0.6.15-1build1) ...
Error org.freedesktop.DBus.Error.Spawn.ChildExited: Launch helper exited with unknown return code 127

(sigh) Now the error is back.

Restarting dbus to see if that fixes the problem...

(sudo stop dbus; sudo start dbus) (close various KDE crash notifications)

(apt-get purge amor ; apt-get install amor)

Still seeing this error:

Error org.freedesktop.DBus.Error.Spawn.ChildExited: Launch helper exited with unknown return code 127

dpkg -l | grep packagekit
rc libpackagekit-glib2-12 0.5.7-0ubuntu2 Advanced library for accessing PackageKit using GLib
ii libpackagekit-glib2-14 0.6.15-1build1 Library for accessing PackageKit using GLib
rc libpackagekit-qt-12 0.5.7-0ubuntu2 Library for accessing PackageKit using Qt.
rc libpackagekit-qt-14 0.6.8-0ubuntu3.2 Library for accessing PackageKit using Qt.
ii packagekit 0.6.15-1build1 Provides a package management service
ii packagekit-backend-apt 0.6.15-1build1 Python APT backend for PackageKit
ii packagekit-backend-aptcc 0.6.15-1build1 C++ APT backend for PackageKit
ii packagekit-backend-smart 0.6.15-1build1 Smart backend for PackageKit
ii python-packagekit 0.6.15-1build1 PackageKit Python bindings

$ grep DefaultBackend /etc/PackageKit/PackageKit.conf
DefaultBackend=aptcc