I can use all of my skins except for one

Hello! Every time I go onto my Minecraft launcher and try to use my skin I created, it says that it cant be saved and I cant use it or duplicate it. I've tried to change it on different versions but still nothing works. I've also tried to change it on the official Minecraft website but it keeps coming out as an Alex skin. I've tried a slim skin and a non-slim skin but it still doesn't work. I've downloaded it and tried it again but still, nothing. Also, I can't delete any of the skins. Please help :/