Cannot upload custom skin on Windows 10 Edition

I am currently running the latest version of Windows 10 and MCW10 edition and am trying to upload a custom skin. I have a skin that I uploaded to the PC edition and Pocket and it worked 100% fine. However, when uploading to Windows 10 Edition with the same file, it says "That's not a Minecraft skin, silly." and doesn't upload. Restarted and everything.