I'm quite the beginner too, hehe.
I think the person above might've been correct. You might want to redirect the message ONLY to the client, as it might be calling on both server AND client.
From my knowledge, you can try putting this before the method that sends the message:
@SideOnly(Side.CLIENT) // DO NOT add a ; after this
And, you might want to import these two things at the beginning of your code:
import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;
I hope I help.