Skin failures (can't be uploaded)

Since a few day I enter to the mob vote, and my skin was different, I decided to reupload what I have (I clarify that my skin is created by myself, so I upload it from my storage) but the system say a message about that is not a skin. I decided to log out and join again, but the skin was lost. I repeated the process about uploading my skin, but the problem still. ¿what can do to fix it?