Error launching minecraft

My minecraft (java edition)  won't launch into the game after the 1.6 update, due to the "netty-all-4.1.25.Final.jar" missing in the io file of minecraft. I have tried updating java on my computer to the latest, and also redownloaded minecraft several times to see if the files appeared. Everytime I press launch, I automatically get notified with the error that the file doesn't exist.