From what I can tell, either your minecraft client or one of the mods in your mods folder is missing a very important file. If you're using mods, try reinstalling any mods that have to do with the player model. If not, then you might need to reinstall forge or minecraft. Try reinstalling forge if you don't have any mods that modify the player model. If that doesn't work, make a backup of your saves and server list then reinstall minecraft.