ok so my game installer wants to run a repair but then it fails?
I got this on steam when my internet connection went down (stupidly kicked the router plug once and once during a storm), though with the lack of internet it probably had nothing to do with steam at all.
I can't remember exactly which files, but Google it and there are some you can delete and then the launcher will start fine. I have to sleep now or I'd find it for you.
I get this every time I have the game client open while the launcher is downloading updates. If this is what's going on for you, close the client and the launcher and reboot (just to make sure there aren't any related processes still running). Then open only the launcher and update. Note: This is a non-steam client.
Battle not with monsters, lest ye become a monster, and if you gaze into the abyss, the abyss gazes also into you. ~Friedrich Nietzsche