CB 2771. The only player online at the time wasn't in the only world which has a few treasure chests in it, so I have no idea...

16:54:31 [SEVERE] Could not pass event PlayerInteractEvent to TreasureChest v8.4.1
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:35)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
at org.maxgamer.QuickShop.Shop.ShopManager.canBuildShop(ShopManager.java:225)
at org.maxgamer.QuickShop.Listeners.PlayerListener.onClick(PlayerListener.java:113)
at sun.reflect.GeneratedMethodAccessor225.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:425)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:35)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
at org.bukkit.craftbukkit.v1_5_R3.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:186)
at net.minecraft.server.v1_5_R3.PlayerInteractManager.dig(PlayerInteractManager.java:108)
at net.minecraft.server.v1_5_R3.PlayerConnection.a(PlayerConnection.java:541)
at net.minecraft.server.v1_5_R3.Packet14BlockDig.handle(SourceFile:46)
at net.minecraft.server.v1_5_R3.NetworkManager.b(NetworkManager.java:292)
at net.minecraft.server.v1_5_R3.PlayerConnection.d(PlayerConnection.java:109)
at net.minecraft.server.v1_5_R3.ServerConnection.b(SourceFile:35)
at net.minecraft.server.v1_5_R3.DedicatedServerConnection.b(SourceFile:30)
at net.minecraft.server.v1_5_R3.MinecraftServer.r(MinecraftServer.java:581)
at net.minecraft.server.v1_5_R3.DedicatedServer.r(DedicatedServer.java:226)
at net.minecraft.server.v1_5_R3.MinecraftServer.q(MinecraftServer.java:477)
at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java:410)
at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:573)
Caused by: java.lang.IllegalStateException: CraftChest is not a chest but is instead CraftBlock{chunk=CraftChunk{x=17z=74},x=276,y=64,z=1191,type=CHEST,data=3}
at org.bukkit.craftbukkit.v1_5_R3.block.CraftChest.getInventory(CraftChest.java:41)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureManager.getLocation(TreasureManager.java:71)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureManager.getTreasureChest(TreasureManager.java:400)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureManager.onPlayerInteract(TreasureManager.java:209)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureChestListener.onPlayerInteract(TreasureChestListener.java:28)
at sun.reflect.GeneratedMethodAccessor191.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:425)
... 27 more
16:54:32 [SEVERE] Could not pass event PlayerInteractEvent to TreasureChest v8.4.1
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:35)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
at org.maxgamer.QuickShop.Shop.ShopManager.canBuildShop(ShopManager.java:225)
at org.maxgamer.QuickShop.Listeners.PlayerListener.onClick(PlayerListener.java:113)
at sun.reflect.GeneratedMethodAccessor225.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:425)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:35)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
at org.bukkit.craftbukkit.v1_5_R3.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:186)
at net.minecraft.server.v1_5_R3.PlayerInteractManager.dig(PlayerInteractManager.java:108)
at net.minecraft.server.v1_5_R3.PlayerConnection.a(PlayerConnection.java:541)
at net.minecraft.server.v1_5_R3.Packet14BlockDig.handle(SourceFile:46)
at net.minecraft.server.v1_5_R3.NetworkManager.b(NetworkManager.java:292)
at net.minecraft.server.v1_5_R3.PlayerConnection.d(PlayerConnection.java:109)
at net.minecraft.server.v1_5_R3.ServerConnection.b(SourceFile:35)
at net.minecraft.server.v1_5_R3.DedicatedServerConnection.b(SourceFile:30)
at net.minecraft.server.v1_5_R3.MinecraftServer.r(MinecraftServer.java:581)
at net.minecraft.server.v1_5_R3.DedicatedServer.r(DedicatedServer.java:226)
at net.minecraft.server.v1_5_R3.MinecraftServer.q(MinecraftServer.java:477)
at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java:410)
at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:573)
Caused by: java.lang.IllegalStateException: CraftChest is not a chest but is instead CraftBlock{chunk=CraftChunk{x=17z=74},x=276,y=64,z=1191,type=CHEST,data=3}
at org.bukkit.craftbukkit.v1_5_R3.block.CraftChest.getInventory(CraftChest.java:41)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureManager.getLocation(TreasureManager.java:71)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureManager.getTreasureChest(TreasureManager.java:400)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureManager.onPlayerInteract(TreasureManager.java:209)
at com.mtihc.minecraft.treasurechest.v8.core.TreasureChestListener.onPlayerInteract(TreasureChestListener.java:28)
at sun.reflect.GeneratedMethodAccessor191.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:425)
... 27 more

I suggest you open an issue with the TreasureChest plugin, this has nothing to do with PlayerHeads.