in your gdb trace the app fails before it even gets to the point where it actually failed in your ubiquity-dm log ...
for valuable debugging data you need to call /usr/lib/ubiquity/wallpaper with a path to a wallpaper picture as the first argument so gdb gets to that point too.
in your gdb trace the app fails before it even gets to the point where it actually failed in your ubiquity-dm log ... ubiquity/ wallpaper with a path to a wallpaper picture as the first argument so gdb gets to that point too.
for valuable debugging data you need to call /usr/lib/