Epic Games commented on the freezing issue which is currently plaguing Gears of War 3, stating to IGN that they are still "working with Microsoft, [quality assurance] and the community" in order to pinpoint the source of the problem, which keeps players from joining any game mode once afflicted.
Possible sources include participating in the game's beta which took place in May, and rejection of the last title update. Once a remedy has been conceived, Epic will out another title update.