If you own the game on Steam, the most reliable fix is to let the client replace the missing file automatically. Right-click in your Steam Library. Select Properties > Installed Files . Click Verify integrity of game files .
You don’t need to reinstall Windows. You don’t need to buy a new PC. Here is the definitive, step-by-step guide to resurrecting mss32.dll. call of duty 2 mss32.dll missing