Comment 8 for bug 173768

I did a bit of debug and I found this:

the problem is in displayconfigwidgets.py line 46 (and next) that object screen passed to the function is null.

but the real problem seems in displayconfig.py @ line 1134 (or 1135)
self.xsetup.getPrimaryScreen() returns null and then assign null to self.current_screen and then pass to the function said above and then produce error.

hope this can help