If your Steam Game is stuck in a loop where it constantly updates and validates itself, and when you try to launch it returns an error referencing corrupted update files, the quickest solution is to do a full reinstall of your game. 

You’ll want to right click on the game in your steam library and then select Delete Local Content from the drop down menu

Once you’ve done this, reinstall your game. Note that doing this installation will remove all user content like settings within the game itself. 

For further assistance with the Steam Client, we recommend contacting Valve’s support team HERE.