How to fix: Unable to read files from a VirtualBox shared host folder

When you want to copy/move from a shared folder (on Windows guests, for example) and it fails with absurd error messages (lots of text or an error about the target being read-only), you are probably running on Guest Additions that no longer match your VirtualBox version.

Fix: install the latest VirtualBox Guest Additions in your guest machine.

Note that you need to make sure you are using the correct ISO.