this worked for me, after many failures. On one of them I ran something like pacman-key --init (from memory - don't bet any money on it) but it didn't seem to do much. After renaming db.lck I ran sudo pacman -Syu and it worked, taking a long time. 85 packages were updated. Immediately after, the software GUI still choked but I rebooted and everything was then clean.
Can't update or install software
