If you bought the game on Steam, this is your first and most likely solution. Steam has a built-in tool that compares your local files against the master copy on their servers.
Sometimes, Antivirus software (like Windows Defender, AVG, or Norton) incorrectly flags game .ff files as threats and quarantines them, causing the game to "not find" them. Exe-cannot-find-zone Black Ops Fix
If the above steps don't work, you might consider uninstalling and then reinstalling the game. This can be a more drastic measure but often resolves issues related to corrupted game files. If you bought the game on Steam, this