Add/Remove... won't launch

I've done a few updates, and now "Add/Remove..." won't actually launch anything. I get a spinning cursor for a bit but that's it.

I tried running gnome-app-install from the Terminal, and I get the following message:

Traceback (most recent call last):
  File "/usr/bin/gnome-app-install", line 30, in <module>
    main()
  File "/usr/lib/python2.5/site-packages/AppInstall/activation.py", line 435, in main
    from AppInstall import AppInstall
  File "/usr/lib/python2.5/site-packages/AppInstall/AppInstall.py", line 62, in <module>
    import distros
  File "/usr/lib/python2.5/site-packages/AppInstall/distros/__init__.py", line 2, in <module>
    from Ubuntu import Distribution
  File "/usr/lib/python2.5/site-packages/AppInstall/distros/Ubuntu.py", line 1, in <module>
    import Default
  File "/usr/lib/python2.5/site-packages/AppInstall/distros/Default.py", line 1, in <module>
    from AppInstall.Menu import SHOW_ALL, SHOW_ONLY_SUPPORTED, SHOW_ONLY_FREE, SHOW_ONLY_MAIN, SHOW_ONLY_PROPRIETARY, SHOW_ONLY_THIRD_PARTY, SHOW_ONLY_INSTALLED
  File "/usr/lib/python2.5/site-packages/AppInstall/Menu.py", line 18, in <module>
    import gst
  File "/usr/lib/python2.5/site-packages/gst-0.10/gst/__init__.py", line 144, in <module>
    from _gst import *
RuntimeError: can't initialize module gst: Error re-scanning registry , child terminated by signal