Was playing around when this suddenly happened:
2012-11-03 17:15:30 [INFO] [STDERR] java.util.ConcurrentModificationException
2012-11-03 17:15:30 [INFO] [STDERR] at java.util.LinkedList$ListItr.checkForComodification(Unknown Source)
2012-11-03 17:15:30 [INFO] [STDERR] at java.util.LinkedList$ListItr.next(Unknown Source)
2012-11-03 17:15:30 [INFO] [STDERR] at ic2.common.AudioManagerClient.onTick(AudioManagerClient.java:105)
2012-11-03 17:15:30 [INFO] [STDERR] at ic2.common.IC2.tickStart(IC2.java:1374)
2012-11-03 17:15:30 [INFO] [STDERR] at cpw.mods.fml.common.SingleIntervalHandler.tickStart(SingleIntervalHandler.java:16)
2012-11-03 17:15:30 [INFO] [STDERR] at cpw.mods.fml.common.FMLCommonHandler.tickStart(FMLCommonHandler.java:116)
2012-11-03 17:15:30 [INFO] [STDERR] at cpw.mods.fml.common.FMLCommonHandler.onPreWorldTick(FMLCommonHandler.java:292)
2012-11-03 17:15:30 [INFO] [STDERR] at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:652)
2012-11-03 17:15:30 [INFO] [STDERR] at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:590)
2012-11-03 17:15:30 [INFO] [STDERR] at bcb.q(IntegratedServer.java:110)
2012-11-03 17:15:30 [INFO] [STDERR] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:497)
2012-11-03 17:15:30 [INFO] [STDERR] at fp.run(SourceFile:818)
I used a diamond drill on some cracked sand (from ExtrabiomesXL) and changed to another slot in my hotbar when the game crashed
Edit: Dont know if it is IC2's fault, but I said somthing about ''ic2'' in the error log