Completely close Steam (check your System Tray to ensure it is off). Restart your computer. Launch Steam and let it check for updates. Log in and try launching the game again. Disable "Steam Input"
If you are staring at this error message, don't worry. This guide covers every proven solution to get Agent 47 back in the field. Run as Administrator
Wait for the process to finish. Steam will redownload any broken components. Restart and Update Steam