Because there's no lwjgl lib at server side, using silicon barn will cause a fatal exception.
Also throwing coin will cause this problem.

MC Crash Report:
---- Minecraft Crash Report ----
// Uh... Did I do that?

Time: 2/24/15 10:11 PM
Description: Exception in server tick loop

java.lang.NoClassDefFoundError: org/lwjgl/Sys
at cn.liutils.util.GenericUtils.getSystemTime(GenericUtils.java:247)
at cn.academy.misc.entity.EntitySilbarn.(EntitySilbarn.java:57)
at cn.academy.misc.item.ItemSilbarn.func_77659_a(ItemSilbarn.java:32)
at net.minecraft.item.ItemStack.func_77957_a(ItemStack.java:268)
at net.minecraft.server.management.ItemInWorldManager.func_73085_a(ItemInWorldManager.java:376)
at net.minecraft.network.NetHandlerPlayServer.func_147346_a(NetHandlerPlayServer.java:841)
at net.minecraft.network.play.client.C08PacketPlayerBlockPlacement.func_148833_a(SourceFile:60)
at net.minecraft.network.play.client.C08PacketPlayerBlockPlacement.func_148833_a(SourceFile:9)
at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:206)
at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:173)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:953)
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:432)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:783)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:646)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.lwjgl.Sys
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:104)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 15 more

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

-- System Details --
Details:
Minecraft Version: 1.7.2
Operating System: Windows Server 2012 R2 (amd64) version 6.3
Java Version: 1.7.0_67, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 366346136 bytes (349 MB) / 1060634624 bytes (1011 MB) up to 1060634624 bytes (1011 MB)
JVM Flags: 2 total; -Xmx1G -Xms1G
AABB Pool Size: 3619 (202664 bytes; 0 MB) allocated, 2795 (156520 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
FML: MCP v9.03 FML v7.2.217.1147 Minecraft Forge 10.12.2.1147 7 mods loaded, 7 mods active
mcp{9.03} Minecraft Coder Pack Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
FML{7.2.217.1147} Forge Mod Loader Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Forge{10.12.2.1147} Minecraft Forge Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
AnnoReg{0.1alpha2} Annotation Registry Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
academy-craft{1.0alpha} AcademyCraft Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
IC2{2.1.484-experimental} IndustrialCraft 2 Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
LIUtils{1.7.2.400_alpha} LIUtils Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available->Available
Profiler Position: N/A (disabled)
Vec3 Pool Size: 31979 (1790824 bytes; 1 MB) allocated, 291 (16296 bytes; 0 MB) used
Player Count: 2 / 20; [EntityPlayerMP['KSkun'/18315, l='academycity', x=116.96, y=82.76, z=43.73](KSkun at 116.96467184140846,82.76090069833738,43.73185349131814), EntityPlayerMP['mkpoli'/1666, l='academycity', x=112.30, y=78.00, z=45.90](mkpoli at 112.30000001192093,78.0,45.90311443823121)]
Is Modded: Definitely; Server brand changed to 'cauldron,craftbukkit,mcpc,fml,forge'
Type: Dedicated Server (map_server.txt)