Edward King

ty Diane Donaldson it has worked for me ^_

Wont that delete all worlds, mods, etc?

This is obviously urgent XD

I've had the exact same issue, I did have the beta launcher but it was fine until around and hour and a half ago. I think (but have no idea) that it could be to do with the nether update as it said updating minecraft before loading the error message. I also deleted the launcher folder in library/minecraft then tried again but the same thing happened. is it possible mojang has an incompatibility with the nether update for Mac users?