After a reboot I could not log back in via the GUI. I got the black screen with a flash of text saying:
WARNING: Failed to connect to lvmetad. Falling back to device scanning. WARNING: Failed to connect to lvmetad. Falling back to device scanning. /dev/mapper/ubuntu--vg-root: clean, XXX/XXXfiles, XXX/XXX
and then reverts back to the login screen.
I did the 'uselvmetad = 0' fix and ran 'sudo update-initramfs -u -k all'
THis got rid of the lvmetad errors, but not the 'ubuntu--vg-root: clean' error. From what I can tell people have fixed it by running 'sudo apt-get install --reinstall ubuntu-desktop', but this did not work for me. I also tried 'sudo apt-get install --reinstall unity' with no luck.
Does anyone know of anything else that I could try?