Comment 22 for bug 973993

I just had the exact same issue as described by Marat above, including the same things in the logs. I don't think I did anything that should have triggered it: it successfully worked this morning, then I shut down and started it up again this evening and the problem occurred. A reboot didn't change anything. What I have done now to make it work is to start the guest session, and from there do a switch user and log in as myself. This time lightdm worked.

In between it working and not working, I didn't apply any updates or anything like that. I haven't reconfigured lightdm in any way, aside from changing the default language and keyboard layout (but that was done a week ago, not today.) The background is the standard one.