Ubuntu – Software Center Won’t start

For a few days now, my Ubuntu Software Center won't start. Ubuntu One also won't connect (not sure if that's related).

When I try launching Software Center from Dash, nothing happens. If I try running 'software-center' from terminal, I get this error message:

2012-03-19 10:26:43,316 - softwarecenter.ui.gtk3.em - INFO - EM's: 17 15 21
Traceback (most recent call last):
  File "/usr/bin/software-center", line 149, in <module>
    from softwarecenter.ui.gtk3.app import SoftwareCenterAppGtk3
  File "/usr/share/software-center/softwarecenter/ui/gtk3/app.py", line 82, in <module>
    from softwarecenter.ui.gtk3.panes.installedpane import InstalledPane
  File "/usr/share/software-center/softwarecenter/ui/gtk3/panes/installedpane.py", line 43, in <module>
    from softwarecenter.backend.oneconfhandler import get_oneconf_handler
  File "/usr/share/software-center/softwarecenter/backend/oneconfhandler.py", line 25, in <module>
    from softwarecenter.backend.restfulclient import get_ubuntu_sso_backend
  File "/usr/share/software-center/softwarecenter/backend/restfulclient.py", line 36, in <module>
    from lazr.restfulclient.resource import ServiceRoot
ImportError: No module named restfulclient.resource

I'm running Ubuntu 11.10 AMD64

EDIT:

It started happening after I install all the dependencies needed to setup an environment to work on the Ubuntu Summit website. I'm assuming something I installed must not have played nice with the rest of my system.