World 64 Crash
The World 64 Crash occurred in World 64 on 9 June 2009 following the "rest" feature update. Any players who logged into World 64 could not log into another world from the account that was logged into World 64.
If the player was on World 64 when the crash occurred and was in a Clan Chat (now known as friends chat), the player would still be in the Clan Chat until they logged into another world, even though the player is not shown in-game.
Aftermath
Even though Mod Emilee, a Jagex Moderator, had stated that Jagex would not be performing a roll-back, they performed a roll-back on World 64 around ten minutes after the crash, leaving some players in a vulnerable spot.
The ten-minute roll-back had a negative effect on players who had just received a decent drop, since it was removed from their inventory. If a player achieved a level within the ten-minute time span of the roll-back, the levels were reverted back to their previous state.