You loaded a 1.7 or newer world in Minecraft 1.6.4.
As always, downgrading is not, was never and will never be officially supported. Please do not run newer worlds in older versions of Minecraft.
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Say something silly, Laugh 'til it hurts, Take a risk, Sing out loud, Rock the boat, Shake things up, Flirt with disaster, Buy something frivolous, Color outside the lines, Cause a scene, Order dessert, Make waves, Get carried away, Have a great day!