It does not affect Uncharted 3.
The error will only occur when the player is in a game. Often before the error occurs, the player's character will freeze and the player will be unable to move, however, it sometimes occurs spontaneously and without warning. The screen will then go black and the error message will appear. After this, the player will be returned to the matchmaking screen. This error can occur in all multiplayer game types.
The player will lose all money earned in the match. However, all medals earned up to the point where the error occurs will still be counted and will appear in the player's statistics, and count towards trophies. If the player has recently quit a match, or recently received another connection error, they will face a quit penalty as the game can not differentiate between a player quitting and a connection error.
As this is not a game specific error, it can not technically be fixed. It affects some players more than others, and is usually caused by a bad internet connection.