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Make an backup and delete the .dat file that has the name of your user (i think it is in one of the folders in the backup).
Download your World and Reupload it again, [ I Hope it will Works ]
Download your world, delete your players file and re-upload your world again. Your inventory and achievements will be lost but you should be able to join your server again.
Upload limit is at 200 Megabytes. If your world is larger than that you can't upload it. You can try to minimize your world's size by deleting chunks using third party apps like MCEdit.
