Java netty: AbstractMethodError

I am recently working with netty and send packets between NettyClient and a NettyServer. Unfortunately, I am receiving the following java.lang.AbstractMethodError:

java.lang.AbstractMethodError: io.netty.channel.SimpleChannelInboundHandler.channelRead0(Lio/netty/channel/ChannelHandlerContext;Ljava/lang/Object;)V
    at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:326)
    at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:313)
    at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:427)
    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:281)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1422)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:931)
    at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:792)
    at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:502)
    at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:407)
    at io.netty.util.concurrent.SingleThreadEventExecutor$6.run(SingleThreadEventExecutor.java:1050)
    at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
    at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
    at java.lang.Thread.run(Thread.java:748)

This error occurs when my client receives a packet from the server. The other way, everxthing works fine. I already checked the version of both programms, and they use the netty-all artifact on version 5.0.0.Alpha2.

The code of my SimpleChannelInboundHandler of my client looks like the following:

package de.jackboyplay.nettyclient.mechanics;

import de.jackboyplay.nettyclient.packets.Packet;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

public class NetworkHandler extends SimpleChannelInboundHandler<Packet>{


    @Override
    protected void messageReceived(ChannelHandlerContext chc, Packet packet) {
        packet.handle();
    }    

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {      
        cause.printStackTrace();
        ctx.close();
    }

}

~JackboyPlay

You should use netty 4.1.x (use the latest release). What you see here is the result of a classpath issue.