Shield update failed - getting error

If you're updating Shield to the newest version and it fails (you get error), that means that something has interrupted upgrading process. 

The errors appear to indicate that the Shield plugin installation during the upgrade broke or was interrupted. It's up to WordPress itself (and the webhost) to perform and complete a plugin installation, and there's no way we can intercede here to address this issue.

The fix for this problem is to completely remove the plugin and then reinstall it from WordPress.org. The plugin .zip file can be downloaded directly from here:
https://wordpress.org/plugins/wp-simple-firewall/

The good thing about WordPress now is that when it does hit this sort of problem, it doesn't completely break the site allowing you to repair such things. You can safely delete the plugin and re-install it.