OK, now I know why these error messages were very familiar to me. I had these error messages for kalgebra as well, and I suspect it is because of SSE2. See more info here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1016658
Version 2.0.8-2 for lightdm-gtk-greeter is very old. But what is this 2.0.8-2+b1 version? I can't find anything about what is this +b1, what are the changes? That might shed some light onto the problem.