Comment 8 for bug 990315

@dkfarns, Please do check the permissions of all the directories /usr/share/xgreeters should be 755, file lightdm-gtk-greeter.desktop is 644 and the /usr/sbin/lightdm-gtk-greeter is 755.

OTOH, symlinking /usr/share/xgreeters/lightdm-gtk-greeter.desktop to /usr/share/xgreeters/default.desktop can also be helpful.