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Here is a fix I found.
ALWAYS MAKE SURE TO BACK UP YOUR WORLD, I AM NOT RESPONSIBLE FOR ANY MORE DAMAGE.
1.) Go to http://mc.42nex.us/ and find your world's seed.
2.) Create a new world with the same seed, map type, and game mode. The Name can be anything.
3.) In your old corrupt .minecraft/saves/(worldname), delete level.dat.
4.) In your .minecraft/saves/players, delete (yourPlayers).dat
5.) Copy your the level.dat from the new world you just created INTO your old corrupt world.
6.) open the minecraft Launcher --> Options --> Force Update.
7.) Congratulations! Your world is now usable again.