Call of Duty Modern Warfare received one of its major updates today with the Season 6 update. However, many fans are not able to play the game as they are greeted with a couple of errors. This issue is mostly experienced by people playing on the PS4. While PlayStation Network is one of the most stable platforms out there, it gets some issues from time to time.
The reason for the Modern Warfare error that the PlayStation network is down. So players are not being able to access their games or use online functionality in many of the games. Some players are also not able to see their games in the library altogether. This will likely be fixed very soon. You can check the status of PSN servers here.