skyline won't let me register my ship and kicks the client in the process

[19:55:24] [Server thread/ERROR] [FML]: There was a critical exception handling a packet on channel skyline
java.lang.NoClassDefFoundError: Could not initialize class esvdefcon.skyline.entity.EntityShip
        at esvdefcon.skyline.chunk.AssembleResult.getEntity(AssembleResult.java:132) ~[AssembleResult.class:?]
        at esvdefcon.skyline.blockitem.TileEntityHelm.mountShip(TileEntityHelm.java:141) ~[TileEntityHelm.class:?]
        at esvdefcon.skyline.network.MsgClientHelmAction.handleServerSide(MsgClientHelmAction.java:65) ~[MsgClientHelmAction.class:?]
        at esvdefcon.skyline.network.ASMessagePipeline.decode(ASMessagePipeline.java:139) ~[ASMessagePipeline.class:?]
        at esvdefcon.skyline.network.ASMessagePipeline.decode(ASMessagePipeline.java:35) ~[ASMessagePipeline.class:?]
        at io.netty.handler.codec.MessageToMessageCodec$2.decode(MessageToMessageCodec.java:81) ~[MessageToMessageCodec$2.class:?]
        at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:89) ~[MessageToMessageDecoder.class:?]
        at io.netty.handler.codec.MessageToMessageCodec.channelRead(MessageToMessageCodec.java:111) ~[MessageToMessageCodec.class:?]
        at io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:337) ~[DefaultChannelHandlerContext.class:?]
        at io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:323) ~[DefaultChannelHandlerContext.class:?]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:785) ~[DefaultChannelPipeline.class:?]
        at io.netty.channel.embedded.EmbeddedChannel.writeInbound(EmbeddedChannel.java:169) ~[EmbeddedChannel.class:?]
        at cpw.mods.fml.common.network.internal.FMLProxyPacket.func_148833_a(FMLProxyPacket.java:77) [FMLProxyPacket.class:?]
        at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:212) [ej.class:?]
        at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:165) [nc.class:?]
        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:659) [MinecraftServer.class:?]
        at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:334) [lt.class:?]
        at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:547) [MinecraftServer.class:?]
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:427) [MinecraftServer.class:?]
        at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685) [li.class:?]