Error:
[Server thread/ERROR] [FML/]: FMLIndexedMessageCodec exception caught
java.lang.RuntimeException: PLAYER target expects a Player arg
at net.minecraftforge.fml.common.network.FMLOutboundHandler$OutboundTarget$4.validateArgs(FMLOutboundHandler.java:125) ~[FMLOutboundHandler$OutboundTarget$4.class:?]
at net.minecraftforge.fml.common.network.FMLOutboundHandler.write(FMLOutboundHandler.java:282) ~[FMLOutboundHandler.class:?]
at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:658) ~[AbstractChannelHandlerContext.class:?]
at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:716) ~[AbstractChannelHandlerContext.class:?]
at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:651) ~[AbstractChannelHandlerContext.class:?]
at io.netty.handler.codec.MessageToMessageEncoder.write(MessageToMessageEncoder.java:112) ~[MessageToMessageEncoder.class:?]
at io.netty.handler.codec.MessageToMessageCodec.write(MessageToMessageCodec.java:116) ~[MessageToMessageCodec.class:?]
at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:658) ~[AbstractChannelHandlerContext.class:?]
at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:716) ~[AbstractChannelHandlerContext.class:?]
at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:706) ~[AbstractChannelHandlerContext.class:?]
at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:741) ~[AbstractChannelHandlerContext.class:?]
at io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:895) ~[DefaultChannelPipeline.class:?]
at io.netty.channel.AbstractChannel.writeAndFlush(AbstractChannel.java:240) ~[AbstractChannel.class:?]
at net.minecraftforge.fml.common.network.simpleimpl.SimpleNetworkWrapper.sendTo(SimpleNetworkWrapper.java:254) [SimpleNetworkWrapper.class:?]
at mcp.mobius.waila.network.MessageRequestTile$Handler$1.run(MessageRequestTile.java:112) [MessageRequestTile$Handler$1.class:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_121]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_121]
at net.minecraft.util.Util.func_181617_a(SourceFile:45) [h.class:?]
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:668) [MinecraftServer.class:?]
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:387) [ld.class:?]
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:613) [MinecraftServer.class:?]
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:471) [MinecraftServer.class:?]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_121]

Description:
This spams in our forge log. not too sure at what causes it but our server was up for about 2 hours and out fml log file size was 182MB due to this spam.

I first posted the error to sponge forge devs just to make sure its maybe not got something to do with that but they told me to send the issue to you.

• Hwyla: Hwyla-1.8.8-B22_1.10.2
• Minecraft: 1.10.2
• Forge: forge-12.18.3.2215

Possible Conflicting Mods (Provide their version, as well)

First, you're outdated.

Second, make sure all clients are on the same version as the server.

Third, dupe of #50