If you have a large pacman update that includes archlinux-keyring package, you may find it fails to install. Remain calm it is a simple fix.
In a terminal run
sudo pacman -S archlinux-keyring
This will update keyring first once finished then update as normal:
sudo pacman -Syyu
You should be good to go.
This only really applies to older ArchBang isos and an install that has not been recently updated.