I have used forge 32.0.71 and 32.0.97 the same message appears in console.
this error appears on entering,on dying and executing commands.
[17:36:26] [Netty Epoll Server IO #2/ERROR] [minecraft/ArgumentTypes]: Could not serialize net.minecraftforge.server.command.ModIdArgument@e1d18d5 (class net.minecraftforge.server.command.ModIdArgument) - will not be sent to client!
[17:36:26] [Netty Epoll Server IO #2/ERROR] [minecraft/ArgumentTypes]: Could not serialize net.minecraftforge.server.command.EnumArgument@1464e82f (class net.minecraftforge.server.command.EnumArgument) - will not be sent to client!