Always backup your worldsyou might want to try (http://www.minecraftforum.net/topic/137381-official-corrupted-save-recovery-thread/)
downgrade to a earlier version of minecraft it's worth a try
or you could try deleting everything in your .minecraft (but you saves texture packs etc.)
and is your world corrupt
for now your going to have to downgrade to try and fix your problem
Satuim Minecraft
Always backup your worlds
you might want to try (http://www.minecraftforum.net/topic/137381-official-corrupted-save-recovery-thread/)