Comment 4 for bug 689997

I'm having the same problem:
Traceback (most recent call last):
File "/usr/bin/software-center", line 111, in <module>
from softwarecenter.app import SoftwareCenterApp
File "/usr/share/software-center/softwarecenter/app.py", line 47, in <module>
from softwarecenter.backend.aptd import TransactionFinishedResult
File "/usr/share/software-center/softwarecenter/backend/__init__.py", line 19, in <module>
from aptd import AptdaemonBackend
File "/usr/share/software-center/softwarecenter/backend/aptd.py", line 30, in <module>
from aptdaemon import client
ImportError: No module named aptdaemon

software-center:
Installed: 4.0.4
Candidate: 4.0.4
Version table:
*** 4.0.4 0
500 http://za.archive.ubuntu.com/ubuntu/ natty-updates/main amd64 Packages
100 /var/lib/dpkg/status
4.0 0
500 http://za.archive.ubuntu.com/ubuntu/ natty/main amd64 Packages

aptdaemon:
Installed: 0.41+bzr646-0ubuntu2.1
Candidate: 0.41+bzr646-0ubuntu2.1
Version table:
*** 0.41+bzr646-0ubuntu2.1 0
500 http://za.archive.ubuntu.com/ubuntu/ natty-updates/main amd64 Packages
100 /var/lib/dpkg/status
0.41+bzr646-0ubuntu2 0
500 http://za.archive.ubuntu.com/ubuntu/ natty/main amd64 Packages