TechRaptor writes, “GTA 4 Error Code 1001 is a mysterious new occurrence that has been popping up when some PC gamers are trying to enjoy Grand Theft Auto 4: The Complete Edition. Unfortunately, this error is stopping them from playing the game entirely, although there does seem to be a temporary fix available.”
Source: N4G PC Rockstar Social Club Error Stops PC Gamers From Playing GTA 4