When I change gdm.conf file, greeter stops working

[syutzy]

As I recall, when GDM starts up, it looks in gdm.conf-custom first, and
then in gdm.conf.  I don't think you should edit gdm.conf, as it might
get overwritten without notice (see the warning at the top of
/etc/gdm/gdm.conf-custom).  So you might be able to get your changes to
stick by putting them in gdm.conf-custom.  



Good reference for what you can do with gdm.conf-custom: 'link'
(http://tinyurl.com/fylrr)



I don't know much more about it than what I've said, but maybe this
will help.


-- 
syutzy