StackableItems ModInventory Error

Could not pass event InventoryClickEvent to StackableItems v1.0.4
Caused by: java.lang.AbstractMethodError
	at org.bukkit.craftbukkit.v1_7_R4.inventory.CraftInventory.setMaxStackSize(CraftInventory.java:482)
	at haveric.stackableItems.listeners.SIPlayerListener.inventoryClick(SIPlayerListener.java:638)
	at sun.reflect.GeneratedMethodAccessor509.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:334)
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
	at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:507)
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:492)
	at net.minecraft.network.NetHandlerPlayServer.func_147351_a(NetHandlerPlayServer.java:2015)
	at net.minecraft.network.play.client.C0EPacketClickWindow.func_148833_a(SourceFile:32)
	at net.minecraft.network.play.client.C0EPacketClickWindow.func_148833_a(SourceFile:10)
	at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:244)
	at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:173)
	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:980)
	at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:430)
	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:798)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:658)
	at java.lang.Thread.run(Unknown Source)