rpi-update is an excellent utility to get all the latest updates and patches for your Raspberry Pi Debian operating-system. But being a utility which downloads and installs all the latest, cutting-edge core OS components it can mess things at times. A recent bad core-patch made Raspberry Pi unbootable for many, after downloading all the files successfully the RPi will fail to boot with the red LED on and green LED flashing 3 times telling a problem with boot files.