Server-side error message

The error I get on the server console is as follows (the client crashes without any kind of error message):

[20:29:14] [Netty IO #1/ERROR] [FML]: NetworkDispatcher exception
java.io.IOException: An existing connection was forcibly closed by the remote host
        at sun.nio.ch.SocketDispatcher.read0(Native Method) ~[?:1.8.0_73]
        at sun.nio.ch.SocketDispatcher.read(Unknown Source) ~[?:1.8.0_73]
        at sun.nio.ch.IOUtil.readIntoNativeBuffer(Unknown Source) ~[?:1.8.0_73]
        at sun.nio.ch.IOUtil.read(Unknown Source) ~[?:1.8.0_73]
        at sun.nio.ch.SocketChannelImpl.read(Unknown Source) ~[?:1.8.0_73]
        at io.netty.buffer.UnpooledUnsafeDirectByteBuf.setBytes(UnpooledUnsafeDirectByteBuf.java:436) ~[UnpooledUnsafeDirectByteBuf.class:?]
        at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:870) ~[AbstractByteBuf.class:?]
        at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:208) ~[NioSocketChannel.class:?]
        at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:87) [AbstractNioByteChannel$NioByteUnsafe.class:?]
        at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:480) [NioEventLoop.class:?]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:447) [NioEventLoop.class:?]
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:341) [NioEventLoop.class:?]
        at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) [SingleThreadEventExecutor$2.class:?]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_73]
[20:29:14] [Server thread/INFO]: Dragennd lost connection: TranslatableComponent{key='disconnect.genericReason', args=[Internal Exception: java.io.IOException: An existing connection was forcibly closed by the remote host], siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null}}
[20:29:14] [Server thread/INFO]: Dragennd left the game