repair let it verify then when it starts to download something click cancel and game will be ready. You don't need to do full repair. Just let it run the first verify.
Did your game update? If so, then close the Launcher and use a Shortcut to the EXE directly, never see this error again. It is the most useless error message, unless of course it won't let the Launcher update the game.
Otherwise, restart the Launcher until it goes away.
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"