Slick-greeter crashes on boot

Well my main-point ATM is, my work laptop is unusable and I’ve to meet deadlines.
(a very painful reminder to finally employ snapshots before updating!)
So far, the workaround (startx) isn’t working either.
I’m considering changing to the old GTK greeter as for a nicer workaround.
(found this: Want to experiment with Lightdm slick greeter? - which gave me the idea.)
And yes, I really like to drill down to the source of a problem, since I just can’t stand that kind of uncertainties of “not seeing what’s really going on” - even though I’m just a user and not a dev. Also to prevent such a problem in the future.
Esp. on an open system.