I fired an arrow at a wolf and it lagged for a while, then my game crashed

---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.

Time: 1/27/13 11:52 AM
Description: Unexpected error

java.lang.NoClassDefFoundError: cpw/mods/fml/common/network/IGuiHandler
	at qz.<init>(EntityArrow.java:125)
	at tb.a(SourceFile:30)
	at ur.b(SourceFile:310)
	at qx.bO(SourceFile:143)
	at ayo.c(SourceFile:311)
	at net.minecraft.client.Minecraft.l(SourceFile:1282)
	at net.minecraft.client.Minecraft.J(SourceFile:582)
	at net.minecraft.client.Minecraft.run(SourceFile:534)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: cpw.mods.fml.common.network.IGuiHandler
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	... 9 more


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at qz.<init>(EntityArrow.java:125)
	at tb.a(SourceFile:30)
	at ur.b(SourceFile:310)
	at qx.bO(SourceFile:143)
	at ayo.c(SourceFile:311)

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [ays['creeperking'/179, l='MpServer', x=79.91, y=67.62, z=248.70]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (56,64,256), Chunk: (at 8,4,0 in 3,16; contains blocks 48,0,256 to 63,255,271), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 5644 game time, 5644 day time
	Level dimension: 0
	Level storage version: 0x00000 - Unknown?
	Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
	Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
	Forced entities: 122 total; [oy['Chicken'/63, l='MpServer', x=11.50, y=76.00, z=319.16], oy['Chicken'/62, l='MpServer', x=8.50, y=76.00, z=321.50], oy['Chicken'/61, l='MpServer', x=11.50, y=76.00, z=319.88], oy['Chicken'/64, l='MpServer', x=13.50, y=76.00, z=320.50], qu['Villager'/85, l='MpServer', x=32.91, y=76.00, z=323.31], pk['Wolf'/84, l='MpServer', x=26.59, y=72.00, z=240.63], qu['Villager'/86, l='MpServer', x=32.50, y=77.00, z=320.50], pk['Wolf'/81, l='MpServer', x=30.88, y=74.00, z=266.47], pk['Wolf'/83, l='MpServer', x=31.50, y=72.00, z=251.50], pk['Wolf'/82, l='MpServer', x=40.50, y=73.00, z=254.94], qu['Villager'/93, l='MpServer', x=40.50, y=79.00, z=324.50], oy['Chicken'/95, l='MpServer', x=46.50, y=78.00, z=320.50], qu['Villager'/94, l='MpServer', x=40.50, y=79.00, z=325.50], oy['Chicken'/102, l='MpServer', x=65.56, y=67.00, z=181.53], oy['Chicken'/103, l='MpServer', x=65.50, y=67.00, z=191.50], oy['Chicken'/100, l='MpServer', x=60.50, y=64.00, z=194.50], oy['Chicken'/101, l='MpServer', x=53.56, y=63.00, z=199.44], oy['Chicken'/98, l='MpServer', x=50.50, y=78.00, z=323.50], oy['Chicken'/96, l='MpServer', x=48.50, y=78.00, z=320.50], oy['Chicken'/97, l='MpServer', x=47.50, y=78.00, z=320.50], pd['Pig'/110, l='MpServer', x=56.25, y=65.00, z=218.59], pd['Pig'/111, l='MpServer', x=73.63, y=68.00, z=203.08], pd['Pig'/108, l='MpServer', x=54.97, y=64.00, z=203.09], pd['Pig'/109, l='MpServer', x=62.81, y=67.00, z=204.09], oy['Chicken'/106, l='MpServer', x=69.50, y=68.00, z=200.50], oy['Chicken'/107, l='MpServer', x=70.50, y=68.00, z=200.50], oy['Chicken'/104, l='MpServer', x=69.50, y=68.00, z=201.50], oy['Chicken'/105, l='MpServer', x=68.50, y=68.00, z=200.50], qu['Villager'/112, l='MpServer', x=61.88, y=79.00, z=316.56], pk['Wolf'/125, l='MpServer', x=84.41, y=67.00, z=240.88], pk['Wolf'/124, l='MpServer', x=84.38, y=74.00, z=263.28], pk['Wolf'/123, l='MpServer', x=86.63, y=69.00, z=249.00], pk['Wolf'/122, l='MpServer', x=83.53, y=67.00, z=262.22], pe['Sheep'/154, l='MpServer', x=153.50, y=67.00, z=263.50], pe['Sheep'/155, l='MpServer', x=154.47, y=67.00, z=260.53], pe['Sheep'/156, l='MpServer', x=154.47, y=67.00, z=260.53], pe['Sheep'/157, l='MpServer', x=155.53, y=68.00, z=259.47], pe['Sheep'/159, l='MpServer', x=157.50, y=68.00, z=281.50], pe['Sheep'/161, l='MpServer', x=157.50, y=68.00, z=281.50], ays['creeperking'/179, l='MpServer', x=79.91, y=67.62, z=248.70], qn['Skeleton'/17829, l='MpServer', x=27.31, y=26.00, z=193.31], qn['Skeleton'/18036, l='MpServer', x=50.50, y=30.00, z=191.50], px['item.tile.sapling.oak'/18009, l='MpServer', x=95.88, y=72.13, z=270.78], px['item.item.dyePowder.black'/17955, l='MpServer', x=23.37, y=61.13, z=203.28], qc['Creeper'/18431, l='MpServer', x=3.50, y=15.00, z=271.50], qc['Creeper'/18391, l='MpServer', x=9.50, y=30.00, z=187.50], px['item.item.apple'/995, l='MpServer', x=121.44, y=65.13, z=258.22], px['item.item.seeds'/1368, l='MpServer', x=59.53, y=63.13, z=182.38], qn['Skeleton'/19520, l='MpServer', x=111.50, y=26.00, z=264.50], qr['Zombie'/19554, l='MpServer', x=103.50, y=22.00, z=198.07], qc['Creeper'/19553, l='MpServer', x=106.99, y=19.00, z=205.16], qc['Creeper'/19513, l='MpServer', x=32.42, y=18.00, z=178.94], qc['Creeper'/19512, l='MpServer', x=24.50, y=27.00, z=187.50], ow['Bat'/19509, l='MpServer', x=0.84, y=15.60, z=264.58], qn['Skeleton'/19791, l='MpServer', x=26.04, y=38.00, z=219.66], ow['Bat'/19839, l='MpServer', x=66.30, y=44.69, z=206.77], ow['Bat'/19838, l='MpServer', x=65.04, y=44.76, z=207.39], qc['Creeper'/19722, l='MpServer', x=22.50, y=23.00, z=283.50], qn['Skeleton'/19717, l='MpServer', x=74.50, y=57.00, z=178.50], px['item.tile.sapling.oak'/19737, l='MpServer', x=93.91, y=72.13, z=261.84], ow['Bat'/19746, l='MpServer', x=51.72, y=30.00, z=196.55], qc['Creeper'/19918, l='MpServer', x=96.50, y=30.00, z=240.50], qn['Skeleton'/19920, l='MpServer', x=38.50, y=48.00, z=240.01], qn['Skeleton'/19921, l='MpServer', x=42.50, y=48.00, z=237.54], qn['Skeleton'/19932, l='MpServer', x=30.50, y=24.00, z=290.50], qc['Creeper'/19952, l='MpServer', x=151.50, y=35.00, z=209.50], ow['Bat'/19843, l='MpServer', x=30.78, y=41.20, z=255.50], qn['Skeleton'/19884, l='MpServer', x=88.50, y=58.00, z=300.50], qn['Skeleton'/19881, l='MpServer', x=19.50, y=24.00, z=270.50], qn['Skeleton'/19883, l='MpServer', x=90.01, y=58.00, z=296.56], qn['Skeleton'/19882, l='MpServer', x=21.50, y=24.00, z=267.50], qr['Zombie'/20080, l='MpServer', x=152.50, y=27.00, z=252.50], qc['Creeper'/20079, l='MpServer', x=145.50, y=37.00, z=273.50], qr['Zombie'/20072, l='MpServer', x=114.50, y=34.00, z=210.50], qr['Zombie'/20070, l='MpServer', x=42.50, y=14.00, z=193.50], px['item.tile.flower'/20061, l='MpServer', x=41.88, y=77.13, z=309.13], ow['Bat'/20051, l='MpServer', x=29.56, y=35.00, z=266.51], ow['Bat'/20044, l='MpServer', x=80.15, y=31.00, z=239.18], ow['Bat'/20046, l='MpServer', x=90.50, y=31.00, z=234.40], ow['Bat'/20041, l='MpServer', x=54.99, y=28.85, z=204.72], ow['Bat'/20042, l='MpServer', x=33.06, y=27.13, z=190.06], ow['Bat'/20039, l='MpServer', x=69.26, y=44.11, z=212.33], qr['Zombie'/20012, l='MpServer', x=8.50, y=23.00, z=183.50], qr['Zombie'/20214, l='MpServer', x=104.50, y=43.00, z=305.50], qr['Zombie'/20188, l='MpServer', x=25.50, y=15.00, z=252.50], qp['Spider'/20191, l='MpServer', x=91.50, y=39.00, z=168.50], qn['Skeleton'/20184, l='MpServer', x=22.87, y=16.00, z=249.50], qn['Skeleton'/20185, l='MpServer', x=26.30, y=14.17, z=261.69], qn['Skeleton'/20186, l='MpServer', x=23.31, y=15.00, z=254.50], qn['Skeleton'/20152, l='MpServer', x=38.50, y=19.00, z=183.50], qr['Zombie'/20134, l='MpServer', x=26.50, y=15.00, z=254.50], qn['Skeleton'/20133, l='MpServer', x=27.50, y=27.00, z=213.50], qr['Zombie'/20139, l='MpServer', x=11.50, y=24.00, z=281.50], qc['Creeper'/20138, l='MpServer', x=28.50, y=15.00, z=249.50], qc['Creeper'/20137, l='MpServer', x=27.50, y=15.00, z=252.50], ow['Bat'/20263, l='MpServer', x=38.25, y=45.00, z=285.06], ow['Bat'/20255, l='MpServer', x=125.46, y=29.92, z=216.67], qn['Skeleton'/20243, l='MpServer', x=89.50, y=36.00, z=284.50], qn['Skeleton'/20245, l='MpServer', x=85.94, y=35.00, z=285.44], qn['Skeleton'/20244, l='MpServer', x=90.50, y=36.00, z=287.50], px['item.item.seeds'/6718, l='MpServer', x=104.28, y=72.13, z=306.28], ow['Bat'/20360, l='MpServer', x=25.04, y=26.16, z=277.38], px['item.tile.sapling.oak'/16291, l='MpServer', x=96.88, y=72.13, z=273.59], px['item.tile.sapling.oak'/18711, l='MpServer', x=94.53, y=67.13, z=272.13], qd['Enderman'/18831, l='MpServer', x=21.50, y=45.00, z=190.50], px['item.tile.sapling.oak'/18826, l='MpServer', x=98.84, y=81.13, z=264.38], px['item.tile.sapling.oak'/18884, l='MpServer', x=96.88, y=81.13, z=266.69], qc['Creeper'/18903, l='MpServer', x=26.50, y=26.00, z=194.31], qn['Skeleton'/15772, l='MpServer', x=85.09, y=48.00, z=243.47], qn['Skeleton'/19067, l='MpServer', x=23.53, y=20.00, z=209.50], qr['Zombie'/19037, l='MpServer', x=95.50, y=31.00, z=257.50], px['item.tile.sapling.oak'/19107, l='MpServer', x=104.44, y=76.13, z=268.13], qn['Skeleton'/19092, l='MpServer', x=61.50, y=41.00, z=269.50], px['item.tile.flower'/15518, l='MpServer', x=91.88, y=68.13, z=185.16], ow['Bat'/19299, l='MpServer', x=28.25, y=26.10, z=279.88], ow['Bat'/19293, l='MpServer', x=49.63, y=18.77, z=177.69], px['item.item.bone'/15465, l='MpServer', x=117.84, y=32.13, z=244.69], px['item.item.dyePowder.black'/15461, l='MpServer', x=55.41, y=61.13, z=188.88], px['item.item.dyePowder.black'/15457, l='MpServer', x=46.81, y=62.13, z=190.88], qn['Skeleton'/19442, l='MpServer', x=55.50, y=43.00, z=243.50], qn['Skeleton'/19443, l='MpServer', x=72.16, y=44.00, z=240.50], qc['Creeper'/19400, l='MpServer', x=6.34, y=23.00, z=176.00]]
	Retry entities: 0 total; []
Stacktrace:
	at ayp.a(SourceFile:281)
	at net.minecraft.client.Minecraft.b(SourceFile:1871)
	at net.minecraft.client.Minecraft.run(SourceFile:548)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 1.4.7
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.6.0_37, Sun Microsystems Inc.
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Sun Microsystems Inc.
	Memory: 58977080 bytes (56 MB) / 238874624 bytes (227 MB) up to 259522560 bytes (247 MB)
	JVM Flags: 0 total; 
	AABB Pool Size: 42040 (2354240 bytes; 2 MB) allocated, 2 (112 bytes; 0 MB) used
	Suspicious classes: ModLoader, ModTextureStatic, EntityRendererProxy[com.moreexplosives.MoreExplosives, EnchantmentMoreExplosivesArrowExplosive]
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	ModLoader: Mods loaded: 1
ModLoader 1.4.7

	LWJGL: 2.4.2
	OpenGL: Intel(R) HD Graphics BR-1004-01Y1 GL version 2.1.0 - Build 8.15.10.2125, Intel
	Is Modded: Very likely; Jar signature invalidated
	Type: Client (map_client.txt)
	Texture Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 2222 (124432 bytes; 0 MB) allocated, 15 (840 bytes; 0 MB) used