21:58:05 [INFO] [PLAYER_COMMAND] creeper_lover77: /f map
21:58:06 [SEVERE] java.util.ConcurrentModificationException
21:58:06 [SEVERE] at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
21:58:06 [SEVERE] at java.util.AbstractList$Itr.next(AbstractList.java:343)
21:58:06 [SEVERE] at java.util.AbstractCollection.removeAll(AbstractCollection.java:336)
21:58:06 [SEVERE] at net.minecraft.server.World.tickEntities(World.java:1197)
21:58:06 [SEVERE] at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:545)
21:58:06 [SEVERE] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:452)
21:58:06 [SEVERE] at net.minecraft.server.ThreadServerApplication.run(SourceFile:490)
21:58:06 [SEVERE] Unexpected exception
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
at java.util.AbstractList$Itr.next(AbstractList.java:343)
at java.util.AbstractCollection.removeAll(AbstractCollection.java:336)
at net.minecraft.server.World.tickEntities(World.java:1197)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:545)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:452)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:490)
21:58:19 [INFO] Connection reset
21:58:32 [INFO] Connection reset
21:58:43 [INFO] Connection reset

The way MCBans is threaded right now is very bad, which can cause issues like this occasionally. It appears to be happening more and more recently, and really should be fixed by using BukkitScheduler to run methods in the main thread rather than calling bukkit methods from another thread.