"Unable to upload skin" when trying to change skin

I was excited to try the new skin changing function in the newest version of the launcher (2.0.760), so I clicked the "Skins" tab and selected the .png file of my skin.

Although my custom skin was shown in the preview (See attached image), when I clicked "Save" I received an error message telling me that it was "Unable to upload skin."

Now when I load my game (version 1.11.2), it displays the Alex default skin in place of my custom skin. Even when I change my skin the old-fashioned way (though minecraft.net), my character is still displayed as the slim-armed default skin (not even the Steve (classic-armed) model).