Error Detected While Installing League

About 5 days ago, it was running fine at first. But when I try to play my 2nd or 3rd game, the match is found, then this window pops up, I get kicked back to the lobby, it says "Repairing Installation," and I can't get into the game. I've updated my drivers, reinstalled it twice already, and even ran it as administrator, but it keeps showing up. Can someone please tell me how to fix this?