flyingblockapi error

[22:06:44 INFO]: [flyingblocksapi] Enabling flyingblocksapi v0.1.4-SNAPSHOT
[22:06:44 ERROR]: Error occurred while enabling flyingblocksapi v0.1.4-SNAPSHOT (Is it up to date?)
java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
	at de.ase34.flyingblocksapi.natives.v1_7_R1.util.EntityRegistrator.registerCustomEntity(EntityRegistrator.java:39) ~[?:?]
	at de.ase34.flyingblocksapi.natives.v1_7_R1.NativesAPI.initialize(NativesAPI.java:43) ~[?:?]
	at de.ase34.flyingblocksapi.FlyingBlocksPlugin.onEnable(FlyingBlocksPlugin.java:40) ~[?:?]
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:250) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:324) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:404) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at org.bukkit.craftbukkit.v1_7_R1.CraftServer.loadPlugin(CraftServer.java:439) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at org.bukkit.craftbukkit.v1_7_R1.CraftServer.enablePlugins(CraftServer.java:375) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.m(MinecraftServer.java:342) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.g(MinecraftServer.java:319) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.a(MinecraftServer.java:275) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at net.minecraft.server.v1_7_R1.DedicatedServer.init(DedicatedServer.java:175) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java:424) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:617) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.7.0_51]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[?:1.7.0_51]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.7.0_51]
	at java.lang.reflect.Method.invoke(Method.java:606) ~[?:1.7.0_51]
	at de.ase34.flyingblocksapi.natives.v1_7_R1.util.EntityRegistrator.registerCustomEntity(EntityRegistrator.java:37) ~[?:?]
	... 13 more
Caused by: java.lang.IllegalArgumentException: ID is already registered: 21
	at net.minecraft.server.v1_7_R1.EntityTypes.a(SourceFile:31) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.3-2-g85f5776-b3024jnks]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.7.0_51]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[?:1.7.0_51]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.7.0_51]
	at java.lang.reflect.Method.invoke(Method.java:606) ~[?:1.7.0_51]
	at de.ase34.flyingblocksapi.natives.v1_7_R1.util.EntityRegistrator.registerCustomEntity(EntityRegistrator.java:37) ~[?:?]
	... 13 more