I got the same output as Psumi :
I don't really know how too fix that but I can provide more informations if that can help to find out.
chmod: cannot access `/usr/share/images/xsplash': No such file or directoryTraceback (most recent call last):
File "./gdm-setup.py", line 327, in <module>
File "./gdm-setup.py", line 183, in __init__
glib.GError: Failed to open file '/usr/share/images/xsplash/bg_2560x1600.jpg': No such file or directory