I'm playing singleplayer, creative and a little bit after the world loads, I get an error that looks like this:
[Railcraft] Loaded 0 saved Anchors
setupTexture: "/mob/cow.png", id: 106
setupTexture: "/mob/chicken.png", id: 107
[Railcraft] Loaded 0 saved Anchors
setupTexture: "/mob/zombie.png", id: 108
setupTexture: "/mob/skeleton.png", id: 109
setupTexture: "/particles.png", id: 110
setupTexture: "/item/largechest.png", id: 111
setupTexture: "/gui/allitems.png", id: 112
setupTexture: "/codechicken/nei/nei_sprites.png", id: 113
setupTexture: "/mob/villager_golem.png", id: 114
setupTexture: "/mob/slime.png", id: 115
setupTexture: "/mob/silverfish.png", id: 116
setupTexture: "/mob/fire.png", id: 117
setupTexture: "/mob/lava.png", id: 118
setupTexture: "/mob/wolf.png", id: 119
setupTexture: "/mob/ozelot.png", id: 120
setupTexture: "/mob/villager/farmer.png", id: 121
setupTexture: "/mob/creeper.png", id: 122
setupTexture: "/mob/spider.png", id: 123
setupTexture: "/mob/spider_eyes.png", id: 124
setupTexture: "/mob/ghast.png", id: 125
setupTexture: "/mob/pigzombie.png", id: 126
setupTexture: "/mob/cavespider.png", id: 127
setupTexture: "/mob/redcow.png", id: 128
setupTexture: "/item/chest.png", id: 129
setupTexture: "/ee/art/sprites/condenser.png", id: 130
setupTexture: "/gui/crafting.png", id: 131
setupTexture: "/mob/sheep.png", id: 132
setupTexture: "/mob/sheep_fur.png", id: 133
Field not found: nn.captureDrops
Field not found: nn.capturedDrops
java.lang.NullPointerException
at acq.a(EntityLiving.java:1094)
at acq.a(EntityLiving.java:887)
at bc.a(SourceFile:124)
at yo.c(SourceFile:251)
at ax.e(SourceFile:77)
at nb.a(SourceFile:55)
at acq.s_(EntityLiving.java:1605)
at acq.e(EntityLiving.java:1452)
at ajr.e(SourceFile:39)
at bc.e(SourceFile:30)
at yo.e(SourceFile:143)
at acq.J_(EntityLiving.java:687)
at yo.J_(SourceFile:155)
at xd.a(World.java:2196)
at xd.f(World.java:2167)
at xd.n(World.java:2049)
at net.minecraft.client.Minecraft.k(Minecraft.java:1871)
at net.minecraft.client.Minecraft.x(Minecraft.java:825)
at net.minecraft.client.Minecraft.run(Minecraft.java:753)
at java.lang.Thread.run(Unknown Source)
2013-06-30 18:06:26 [sEVERE] A critical error has occurred.
java.lang.NullPointerException
at acq.a(EntityLiving.java:1094)
at acq.a(EntityLiving.java:887)
at bc.a(SourceFile:124)
at yo.c(SourceFile:251)
at ax.e(SourceFile:77)
at nb.a(SourceFile:55)
at acq.s_(EntityLiving.java:1605)
at acq.e(EntityLiving.java:1452)
at ajr.e(SourceFile:39)
at bc.e(SourceFile:30)
at yo.e(SourceFile:143)
at acq.J_(EntityLiving.java:687)
at yo.J_(SourceFile:155)
at xd.a(World.java:2196)
at xd.f(World.java:2167)
at xd.n(World.java:2049)
at net.minecraft.client.Minecraft.k(Minecraft.java:1871)
at net.minecraft.client.Minecraft.x(Minecraft.java:825)
at net.minecraft.client.Minecraft.run(Minecraft.java:753)
at java.lang.Thread.run(Unknown Source)
2013-06-30 18:06:26 [sEVERE] 41 mods loaded
Optifine OptiFine_1.2.5_HD_S_C6
Minecraft Forge 3.3.8.164
FML v2.2.106.176
Forge Mod Loader version 2.2.106.176 for Minecraft 1.2.5
mod_CodeChickenCore : Available (modpack.jar)
mod_MinecraftForge : Available (modpack.jar)
mod_NotEnoughItems : Available (modpack.jar)
mod_ReiMinimap : Available ([1.2.5]ReiMinimap_v3.2_04.zip)
mod_IC2 : Available (industrialcraft-2-client_1.97.jar)
mod_IC2AdvancedMachines : Available (AdvancedMachines_4.0_client.zip)
mod_BuildCraftCore : Available (buildcraft-client-A-core-2.2.14.zip)
mod_BuildCraftBuilders : Available (buildcraft-client-B-builders-2.2.14.zip)
mod_BuildCraftEnergy : Available (buildcraft-client-B-energy-2.2.14.zip)
mod_BuildCraftFactory : Available (buildcraft-client-B-factory-2.2.14.zip)
mod_BuildCraftTransport : Available (buildcraft-client-B-transport-2.2.14.zip)
mod_AdditionalPipes : Available (buildcraft-client-DA-additionalpipes-2.1.3.zip)
mod_ComputerCraft : Available (ComputerCraft)
mod_RedPowerMachine : Available (RedPowerMachine-2.0pr5b2.zip)
mod_ccSensors : Available (ccSensors-client-MC125-B017pr1.zip)
mod_CCTurtle : Available (ComputerCraft)
mod_EE : Available (EE2ClientV1.4.6.5.jar)
mod_EnderStorage : Available (EnderStorage-Client 1.1.3.zip)
mod_IC2NuclearControl : Available (IC2NuclearControl_client_v1.1.10b.zip)
mod_ImmibisCore : Available (immibis-core_49.1.1_for_1.2.5-client.jar)
mod_InvTweaks : Available (InvTweaks-1.41b-1.2.4.zip)
mod_MAtmos_forModLoader : Available (MAtmos_packaged.zip)
mod_ModularForceFieldSystem : Available (mffs_rev7_for_1.2.5-client.zip)
mod_IC2_ChargingBench : Available (mod_chargingbench-client-1.95b-1.2.5-r1.zip)
mod_CompactSolars : Available (mod_compactsolars-client-2.3.2.10.zip)
mod_IronChest : Available (mod_ironchests-client-3.8.0.40.zip)
mod_RedPowerCore : Available (RedPowerCore-2.0pr5b2.zip)
mod_NetherOres : Available (NetherOres_Client_1.2.1.zip)
mod_PowerConverters : Available (PowerConverters_Client_1.3.4.zip)
mod_Railcraft : Available (Railcraft_Client_5.3.3.zip)
mod_RedPowerControl : Available (RedPowerControl-2.0pr5b2.zip)
mod_RedPowerLighting : Available (RedPowerLighting-2.0pr5b2.zip)
mod_RedPowerLogic : Available (RedPowerLogic-2.0pr5b2.zip)
mod_RedPowerWiring : Available (RedPowerWiring-2.0pr5b2.zip)
mod_RedPowerWorld : Available (RedPowerWorld-2.0pr5b2.zip)
mod_TubeStuff : Available (tubestuff_49.1.2_for_1.2.5-client.jar)
Balkon's WeaponMod : Available (WeaponMod.zip)
mod_WirelessRedstoneCore : Available (WR-CBE Core-Client 1.2.2.3.zip)
mod_WirelessRedstoneAddons : Available (WR-CBE Addons-Client 1.2.2.3.zip)
mod_WirelessRedstoneRedPower : Available (WR-CBE RedPower-Client 1.2.2.1.zip)
mod_ImmiChunkLoaders : Available (zdimensional-anchor_rev3.2_for_1.2.5-client.jar)
If you have found another thread where this is explained, please link me to it, as well.
Thank you.
Also, this does not happen in survival multiplayer.