Steam will now scan your installation folder. It will compare your local files against the master files on the Steam server. If steam-api.dll is missing or altered, Steam will automatically re-download the correct, pristine version. Once the process finishes, try launching the game.
If verifying the files fixed the problem, but the error returns after you restart your computer or launch the game a second time, your antivirus is the culprit. fallout new vegas steam-api.dll
: The file was accidentally deleted or quarantined by antivirus software. Steam will now scan your installation folder
Check your "Quarantine" or "Protection History." Antivirus programs often flag this DLL as a false positive, especially if you are using a modified version for a script extender. : Steam will automatically re-download the correct